A lot of comments are bringing up top athletes as a counterexample, which leads me to believe they don't understand what a high-level training regimen is actually like. I have a relatively unique persepective on this[1], so I thought I'd clarify a few things. Any sport is both mentally and physically exhausting, and it only gets more strenuous as you reach the higher levels. Nobody can keep this up all day, every day…
Someone is presumably paying good money for them to be there, and by the time they become professionals, they'll have spent XX years already in training, with someone else presumably working and funding their entire stay/attendance.
This then presumes that those kids who do actually make it to the pro circuit aren't then the ones that also have the advantages and put in extra above and beyond the other kids (and with a little bit of luck on top).
Now, I don't know what other people's life was like growing up. I mentioned in my other comments that conceivably there are some kids who had parents who both supply them with knowledge, fund their study, their lifestyle, gave them opportunities and access, and that such people might subsequently have greater abilities than myself, and maybe those people will become top notch coders even with some hobbies and time on the side.
But no one is paying to have me (or others) learn to code or update my skills. No one is paying to send me to a training camp or academy. I taught myself computers and I know many others did too. There was/were limited academies when I grew up, and there aren't any pros for us to learn from except ourselves now.
Many of us aren't paid to do our coding or our study, many workplaces or academies aren't even interested in that kind of coding or study.
And, of course we burn out. No shit.
But that doesn't mean that if you don't want to become top rate you don't have to put in more than a paltry 8 hour workday. Indeed, EVERY decent coder I've known has done it. Not a single one I know hasn't. I have not met any decent coder that hasn't been doing their own thing on their own time and that wasn't interesting and successful in teaching themselves in their own time.
The tennis kids have someone else to put in a workday so they can then spend hours per week at a leisure activity.
Unless we are very lucky, we spend our work/school day so we can ferret away the time and resources to focus on the stuff we actually value, and then that knowledge then gets transmitted back to the workplace...