Why would there need to be more than what it required? No skill should be forced in. You could have Persuasion (let's this is context sensitively used as sweet talking and intimidation with different attributes used as governing factors... say, body for intimidationa and cool for persuasion), Deception and Seduction for specific purposes and that's it; and still have checks for other skills for knowledge about them.
Or, the game will simply handle that via your character stats and a tree of faction relationships, directly. It's not something that needs a "skill tree" to make sense, and not something that is rigid enough to require its own stat, as a
video game adaptation of is not the same thing as the table-top version of an RPG. It can't work that way.
Hence, for PnP, my character's backstory may set my "base" ability to to speak street vernacular really well. It's naturally how my character speaks. Because I also chose the "Street Kid" skill, I can now talk it up with the average tough on the street and feel like I'm from their world and I get how it works. If I encounter a gang member I helped out in the past, and I'm going to try to talk them out of killing another NPC, the GM will simply handle that situation organically:
GM: "Alright, but that's going to be tricky, so what will you try to use, Reason or Intimidation?"
Player: "Reason. 'Look, man. Think this through, yo. This meat can die any day -- doesn't have to be now. And it would mean money to me to give a few days to rest. Besides, you still owe me for that door kicking we did last week, yo.'"
GM: "Ah -- good point. Alright, what are your chances?"
Player: "I've got 15 in Reason, +4 Intelligence modifier, and +5 for Street Kid -- so: 24."
GM: "Add +10 for bringing up the fact the guy still owes you and roll."
Player: (Grabs a d20 and rolls a 10. 10+4+5+10) "29!"
GM: "Yeah, you see him start nodding before you're even done talking. He doesn't look happy about it, but he holsters his gun..."
Now,
the exact same thing can be accomplished in a video game -- but we don't need separate skills for Reason, Intimidation, Street Kid, and numbers to represent the dialogue attempt
to be visible. All the game needs to do is check certain flags according to the player's past choices and pathway through the game. Behind the scenes, the game will use its own system to go:
[Dialogue choice selected.]
Base success value =
40
Player stats:
Intelligence = 12
Cool = 10
Street Cred = 18
Modifier: Faction = 5
Modifer: Quest Resolution (Door Kickers) = 10
Modifier: Damage to Faction = -3
Final Value = 12+10+18+5+10-3= 52
52>40 = Success!
Proceed to Dialogue Option 4.
None of that needs to be displayed in-game as a bunch of tables and charts and assigned points. It just needs to be calculated by the game's engine in the background, leaving the experience on-screen as fluent and cinematic as can be mustered. Just like in real life, all of the considerations are there, but we simply say something and someone else will have a reaction to it.
For PnP, this type of thing often benefits from having more fleshed out skill trees with numerical stats that can be combined every which way depending on the situation. And it ensures neither the GM or Players'
human minds override what would be more sensible for a given scenario when it pops up. For a
video game, every available option must be pre-determined and specifically coded into the software ahead of time, and computer will simply do all applicable math at the time and provide a final result in milliseconds. Thus, that limitation can be offset by having the experience remain cinematic and organic. It's pointless to clutter up a screen with skills and values that the player will never need to bother actually interacting with during the execution. It's not that these things are not there or not factored in -- it's just that video games don't need to make all of these values
visible.
For combat skills, however, there are a lot more options that are not based on particular story, plot, or character interaction elements through gameplay, but more on what a character chooses to focus on and build. Hence, there might be 30 options for weapon skills, but only 3 options for Speech skills, and 5 options split between Rogue skills and Hacker skills. However, in the end, a player's character will be defined by a total of 6 skills. While we have
options for 30 different types of "combat" oriented skills, only a pure fighter will select all 6 of their character's major abilities from that tree. And it's perfectly possible to create an equally versatile gameplay experience choosing
only non-combat skills, as well.
Why would you add skills that you know you aren't going to be giving any usefullness?
The point is not about "having as many skills as possible because skillz is cool", but more like "having as many skills governing the gameplay-essential tasks and activities as is reasonable and effective for the feel of the gameplay". So that what you do in the game is more than just doing it because you can.
One needs only look at CP2020 pg 45 to see a number of skills not related to combat.
The problem, and it's a HUGE one, is incorporating these skills into an video game. While not impossible, it'd be far more time/effort then it's generally worth.
Precisely. So, to make combat work and let the player understand exactly what they're investing in and how that will affect their combat performance, do I
need a large tree of skills? Yes! Just like in real life, combat is fairly particular and dangerous, and people are trained along very specific pathways of gear and skills to accomplish very specific combat roles on the battlefield.
Far less so with public speaking, for example. If I learn how to enunciate properly, speak slowly enough that my words are clear even over distance, and project the right level of emotional energy into my words at the right times -- I can now play any house! I can speak at a wedding, a political rally, to a bunch of kids about healthy eating, or narrate a documentary about the breeding habits of dinosaurs. It's all the same skill. This doesn't require a skill tree with 15 options on a menu. It requires 1 or 2.