1. To work on a stable product. At startups, I never got to work on the same product through multiple versions across several years. I wanted the experience of launching something, then iterating on it. To become an expert in a market and develop long-term relationships with users or customers. All the startups I'd been in either failed or pivoted within a couple years, and all the consulting work I'd done with startups was always parachuting in to help on something and then leaving soon after.
2. As mentioned, to work on something more fulfilling than SaaS products. No shade on anyone who works on these, they are often really fun and exciting. But, my last job was trying to sell a yearly $60k subscription service to companies so that they could lay off members of their team and replace them with our product. My current job is helping scientists who are researching a very nasty disease that has directly affected my family. Not only can I explain what my current company does a lot more easily, I can honestly say I am there for more than the money or how good it looks on my resume.
3. Less work. My previous job had been described—by leadership, with a wink and a nod—as 'a pie eating contest where the prize is more pie'. That is, work really hard until we get PMF, then if we get that, work even harder so that we can get acquired. At the end of that, maybe my stock options would be worth something, but the owners and investors certainly would get a nice payday. I'm in my 40s now, I'm not going to work myself like a dog anymore, I kinda just want to have a nice, easy job, as long as I can feel good about doing it.