The ultimate goal for any martial arts student has to be getting the black belt. When a student may lose motivation and feel 'it's quitting time', any excuse will do to justify it (it may be a disguise for failure). Sure, there are those who feel martial arts might not be for them in the long term, and that is OK, but there are many who may regret. I've taught over 1500 students so I have seen this many times.
The 'quitters' usually return to the scene, some time later because the motivation returns. Unfortunately, these people quit again because of not being able to settle in and not finding it easy to pick up again from where they last left off.
Time is a common excuse and it really is up to the individual to decide what to do with their time. Maybe, if they look at the Instructor's schedule people might not think they have it bad after all.
When I first started training in traditional Karate (Budokan) with 20 other white belts, I was the only one who stayed and got my black belt. A few yeas later, a new student approached me and said he started training the same time I did as a white belt. He went on to say he was astonished I was a Black Belt and if he stayed he could've been also wearing a black belt. I never saw him again!
If anything, stay on to keep fit. Why would you even bother going to general fitness classes (because the weighing scales are lying to you again) when you know it will only be a matter of time you will get bored and quit.
It's true, not everybody makes it to Black Belt! Only, the ones who want to, will. These are the special kind of people.
Don't be a K-mart special – 'here today, gone tomorrow'.