And beyond Larry and Sergey, there seem to be a lot of founders who are basically retired? What do they do all day? How do they transition from what were probably incredibly busy and choreographed days?
Larry is suffering from an autoimmune disorder - likely Hashimoto's. Dude developed PageRank and built one of the most successful companies on Earth. He can probably sit back and focus on philanthropy and flying cars...
CNN agrees with you, saying it's Hashimoto's thyroiditis, the most common cause of hypothyroidism. Page has publicly attributed his hoarser, softer speaking voice to vocal cord paralysis, although the original Google+ post that the stories about it seem to have used as their source is no longer available.
Business when you have unlimited money to your name to deploy is very different than when you are starting out.
For any self respecting man the process of doing press is a pain in the back. You see it in every domain ranging from sports to music to movies.
Ranging from Aaron Judge to Wayne Gretsky they will all tell you the same, the absolute hatred for interviews and doing press of any kind, but they are employees and the front office of their Franchise is forcing them to do so.
Once you are a billionaire those dynamics don't apply anymore, you don't have to convince bankers or venture funds or investors or the public anymore. It's a one man show and the only goal is to keep morale high among employees.
Yeah, he gets to test the random ideas he has. Like "why does Twitter have thousands of employees?", or "why does it cost so much to drill holes?" or "how hard can it be to build rockets?" and so on. The rest of us have to theory craft and argue on forums instead of doing it for real.
Larry is mostly reclusive from what I've read.
Sergey is working on bringing back blimp travel with his Lighter than Air (LTA) company: https://www.ltaresearch.com/