What is an "accomplished" skier? Where was the motivation coming from in the first place?
As @segbrown has pointed out, skiing is a major PITA with high barriers to continuing when other interests come along. You don't have pushy parents anymore, and you don't have to listen to aggressive coaches demanding impeccable performance and endless boring drills.
I still ski. A lot. Often alone. But I exist on the fringes. I don't have kids and I live in some of the best ski country in the world. I was, for many years, so self-motivated to learn how to do it better and have more fun while doing it that I subjected myself to the training required to become a fully-certified professional instructor, despite having full-time non-skiing employment. I didn't have parents or coaches pushing me. Initially, it wasn't a social motivation, although there came to be a time when most of my winter social life, such as it was, revolved around the ski school.
But now I no longer teach. I find my social ineptitude has resurfaced with a vengeance, so I ski alone or with my wife. I am guilty of picking my days. Ski the good stuff, or don't bother. My seasonal count, while high by any normal standard, is way down. Warm weather and sun has more appeal than it used to.
So what has happened? Motivation is dropping. When I was a paid instructor, it was a matter of pride to be able to ski well in crappy snow. Now, it doesn't seem to matter as much, although I've been known to go make turns in 6" ice-crusted goop just to prove (to myself, since no one else cares) it can be done.
Maybe I've just gotten lazy. I think about what I used to go through in order to ski (and not very well, at that), and realize I certainly wouldn't do it today.
Motivation is huge. Skiing is social, skiing is challenging, skiing is family. If your friends (assuming you have any after years of skiing) don't ski, if your family doesn't want to ski or has grown up and left home, if you're becoming wary of the possible consequences of some kinds of challenges, motivation will decrease.
To keep skiing, it may be necessary to find new motivation. Many find motivation to do something else.