I don't know if they have an improvement-focused mindset, but many of the adults I know who only play matches have been at it for more than 20 years. Doing a lot of match play isn't a magical technique for improvement, though I agree that sufficient match play is an important factor for those who wish to improve.These people on the rec courts have only been playing a few years I would have thought, or have not adapted an improvement-focused mindset.
If you have an improvement-focused mindset best to play more matches, doing 50% drills 50% match play for years is throwing the baby out with the bathwater IMO
What the proper balance is between match play/practice sets and drilling isn't easy to determine, and I believe it varies based on the individual and his personality/strengths/weaknesses.
It seems that all-or-nothing advice is very popular on this board.