I, for one, would be completely nonplussed if a person told me they were taking up any activity, yet had no intention of improving at it. This would be true for not only physical activities like the martial arts, running or tennis, but for everything from video gaming to needlepoint and knitting.
The questions then, relate not only to personal motivation for doing an activity, but to how much one wishes to improve. This will depend upon their physical and mental abilities and deficits, along with their ability to dedicate time and resources, along with handling the other priorities in their life. Priorities can change dramatically over time, as well. A martial arts journey, like any other, doesn't take place in a vacuum where it can travel a straight and orderly path.
For instance, in my own case, I initially took up a martial art in 1991, when my Reserve Unit was activated and I was at Ft. Sam Houston during Desert Storm. I was working out and running, and was as fit as I've been in life, but much of that was done during regular PT. I was going stir crazy during my off duty hours and a civilian I worked with suggested I take some lessons at his dojo. I did, and enjoyed myself, and got rid of a lot of stress for the three months or so I took lessons. The sensei suggested if I wanted to continue in martial arts, to look for a Kenpo dojo when I got back home.
Once I finished college and located where I live now, I looked up a Kenpo dojo (conveniently, one of the only dojos in town at the time) and began training again. It was great stress relief while in law school and as a young assistant prosecutor. I also enjoyed the discipline, learning new skills and knowledge, and more. I progressed fairly rapidly until two daughters, career responsibilities, and the National Guard started intervening. On the cusp of training for my black belt, my frustration level, and that of my instructor, were such that I decided a break was in order. As I have mentioned, I am only now getting back to it after many years. How good was I when I was training regularly? I can only say once I was a brown belt, I could spar effectively against others who competed regularly at tournaments, as well as two who fought and did well in NASKA and internationally.
The above isn't intended to speak of or brag about myself, but to point out a few things, using the best example I know. People enter the arts for a variety of reasons, often having nothing to do with lifestyle change. Taking the step does mean they likely don't wish to be stagnant in their involvement, but wish to make some progress. Once they do, their priorities can indeed change over time, for a number of usually legitimate reasons.