Small companies probably can't afford to pay taxes for everyone's 83b elections, nor can they afford the 401k match or the other missing perks. After all, if they could afford to compete on cash comp with big tech cos, surely the founders would rather do that and preserve their own equity stake.
But with exits taking longer and longer, such an exercise scheme lets rank and file employees preserve some small upside that they have earned themselves, and not worry about hurting their career by being forced to wait for an exit.
I think I generally agree that employees get a pretty bad deal. I think it used to look better, but these days you can make so much more money so much faster working at Google than you can at a random startup.