I think it is left overs or a quick fix from the initial design, when it was going to be an RPG. But as the game turned to an adventure game, it didn't really make sense with all the choices in the character creator. But now that they had already shown it and told people that it was an RPG first, it would have really pissed off people had they completely removed it.
So I think they threw it in there as a quick bandage trying to cover the fact that the game weren't really going to be the RPG game people thought, but telling people that they turned it into life path, which would play into the game would seem like the feature hadn't been removed, but simply "improved". Also I think it's fairly obvious from the lack of content that relate to life path, mostly it's a few dialog options which doesn't make any difference or its a couple of missions.
If you compare the current life path options, with the amount of different options you had in the initial design of how to create your character, it's pretty clear that a lot more thoughts and options had to go into this and in making the game more of a player choice driven experience with a reactive world, rather than the player being forced on a linear path.
Also my guess is that the first mission they presented with the Maelstroms was how they intended the missions to work originally. But when Keanu and Silverhand got added, the whole game turned from the initial player choosing their "life path" as in the initial design. To just choosing some generic life path as it is now and everyone forced into the Silverhand life path and everything had to revolve around Silverhand and in the case life path didn't matter, because the game is not really about the player, but Silverhand.
The player is at no point involved in the Adam Smasher story, it's about Silverhand. The Heist is just a generic mission where the player does something wrong against the Arasaka, and then it's somehow weirdly turns into the Araska being the bad guys and Silverhand and his old crew want revenge, V have nothing to do with it, except being stuck with Silverhand. Imagine Silverhand was removed straight away after the Heist and there would be absolutely no motivation for V to get involved in the main story at all and hold a grudge again Arasaka or Smasher.