I'd presume that the reason is simply that modding is time intensive and if you have a job/family you rather put the effort into your own project.
That's pretty much how my relation with Freespace had been for the longest time. For the first couple of years, I was almost exclusively a player, crunching campaign after campaign, only FREDding a handful of missions here & there. Then 3.6.12 came around, broke some of my missions, prompting me to shift my modding habit into higher gear. I spent the next 3-4 years splitting my time rather evenly between modding & playing, until my Master's final 2 years. As my free
(space) time became more & more precious, I tended to favor modding over playing, and only stopped everything after the whole "you need to play to have an opinion" thing back in early 2017.
I only eased beack into the game in late november - exclusively as a player this time, going through FS2 with surprising ease. Right now I'm re-playing through JAD 2.21 - JAD 2.22 (I don't think I every finished 2.22), then it'll either be BtA or WCS Open.
Still, the call of modding is
still strong, I always get tons of ideas while doing random stuff, and some of them might even be practical

. But for now, I shall apply Willpower™ and stick to playing !