Doesn't address the fact that you can't hack MaxTac or Netrunners.. Again, at this point I really doubt this was on purpose. Canon or not, it reduces the freedom in the game for a good portion of characters for no real reason.
You don't seem to have a RED tag on your name, and I'm not gonna just completely ignore a possible bug or unintended feature just because someone said it's intended. Just reporting what I see.
Because its called "internal consistency". With the hacks themselves, if they were able to be used on cops every gang with a netrunner in the city would do the same thing. Gangs and Corps in game cannot hack cops; Ergo V cannot hack cops, so you the player cannot hack any kind of cops period. This is exactly the same as the fact you cannot hack civilians. It has zero bearing on the storyline or the actual gameplay as the cops are nothing more than "filler". You walk away and they ignore you and do not give chase. They are only there to "protect civilians". Not to do any real detective work, or solve major crimes.
In cannon it is because the cops are dirty, overstretched, and have no real power over corporations or gangs. The city is rife with crime, and corpo subterfuge of which you are just a minor blip. That is why (in game) the cops do not bat an eyelid at you when you are "interviewed" at one point and tell them you are a Mercenary.
In canon MaxTac have tech direct from corps that cannot be hacked. The gear has AI systems that block any intrusion attempt and hardened coms networks that have top level security with "dwellers" on the whole system 24/7. This is intended to keep them as the second most dangerous force in the "world" (the first being corpo elites - ie Adam Smasher). The gear the player gets is "street legal" cyberware, which is the same for most gangs. A few instances in the story have specific points where gang's get a hold of high level tech, and that's where you come in.
In game there is zero need for you to be able to hack cops. You are never actively forced to engage them in any way at any point in any mission. Sure they might come after you for doing stuff, but they never are a target for the various factions in game. There is as far as I know just 1 minor side mission involving 3 cops that you can chose to combat specifically.
Anyone can use a smartgun, there is no restricton on usage. Just on its homing capablity and target linking. Which can be done with a simple tattoo and/or smartglass (as shown by the Tyger Claws).