IT people just drop out. The simple cases become managers or architects. The more advanced cases start a bakery, go work in a call center. One of the most extreme cases was a very intelligent, very cynical, very anti religion guy who just quit without warning and joined the hare chrisna. We got photos from him in red clothes doing some kind of ritual. Huh?
A big part for me is that IT just doesn't learn. Every 5 years, a new generation pops up, invents completely new tooling, and makes all the mistakes from the previous generation. Now your knowledge is obsolete, and after you relearn everything your tooling is worse than where you started. Enter a few years of slow tooling maturisation with a very predictable outcome, after which a new generation pops up, declares the existing stuff too complicated, and reinvent everything again. 35 is 4 or 5 of these cycles, bringing to front the huge wastefull uselessness of it all. Learning your whole life is a nice slogan, but becomes very pointless.
The survivors that continue in IT, deal with it somehow. You enter a new cycle knowing it will be change but not much advancement, and don't learn the stack as deep as you used too. You get a life outside IT: Kids, hobbies, social events. You let the youngsters run before you, smile when they do better than your old tech would, and compare with older tools when they get stuck. And you keep some of your tech enthousiasm just for the hell of it.