I suspect it's much more a time gulf than a skill gulf.
I love AoC as well and don't so much burn out but find that after a week of coding for fun in the evening a mountain of real world responsibilities start piling up, especially around the holiday season.
When I was in undergrad I had virtually no family responsibilities during December and a large amount of free time when classes ended, so it would have been easy to spend hours a day on AoC. Many younger, single professionals are likely in the same situation.
I think for most adults with family responsibilities and full time jobs (and likely a range of side projects that also need attention) that first week of December is a rare lull, and a great time to solve a bunch of fun code problems. After that more and more other things take focus as the holidays approach.