It's not difficult at all to become one, and the work involved in being a CEO is not particularly difficult in comparison to senior technical work at all. The only thing that is harder about being a CEO is the responsibility. I'm sure being the CEO of Microsoft or whatever is plenty difficult and demanding in many ways, but most CEOs are not that, and speaking just from experience most CEOs and CTOs are clueless morons.

With that said, I've been programming for 25 years and I've only been a CEO for 3, so take what I said with a pinch of salt.

I do think people overestimate titles like this a lot, though, and it really comes down to what the company actually does and what is demanding for that company at that position/role. The CTO of a some-bullshit-as-a-service company may as well be straight out of college, because they're likely doing something trivial that literally anyone (including LLMs) could put together. The CTO of a well-used and reliable streaming service that handles a meaningful part of the world's Internet traffic is obviously solving a more interesting and demanding problem, and their decisions are going to be more important.