When I was young I found great players to always be an inspiration. My thought process was, maybe someday I can play like that.
Towards the end of my playing career, my organization hired a young bass player who had more technique than I will ever have. He influenced me to become a better player, but I was also faced with the limits of my talent and drive. It was clear I would never be able to do what he could do...and while I was approaching the down hill slope, he was still climbing the mountain and getting better along the way.
I actually crossed over to audio within a few years of his arrival, and a blast. My decision was influenced by a range of factors, and not just the new player's superior talent and skill. Probably the biggest factor is my skill level had risen well beyond the baseline required to do the job. Also my organization had lost several of its best players and the musical excellence had significantly declined.
In my experience, a desire for continued musical growth is a huge part of why musicians continue to play. Once that need/desire for growth is lost, you're probably rapidly approaching a point where the joy of playing will leave you.
I don't really feel too bad about it. We each have a our own unique talents and limitations. One of my strengths is that I tend to pick up things fairly quickly. The weakness is my skill-level tends to plateau before achieving excellence. The idea is that I tend to run well ahead of others in early development. The few that stick with it, eventually catch up and then pass me. However, I consider my musical skill above average.
I tend to enjoy variety rather than being a specialist. I could never be a top jazzer, classical, commercial, etc player. However, I was pretty good at all of them. The trick is to find a niche where your unique mix of interests, talents, and abilities are useful and valued. I was lucky enough to find such a niche. So I had what I consider to be a relatively long and successful career as a full-time professional musician.
To this day, I lack interest in being an active bass player. I still practice and buy new stuff, but the fascination with learning music and drive to perform is no longer with me. I could do it if I had to, but it would not bring me the intrinsic joy I used to feel...I.E it would be work.