It's a weird subject for academic study in the first place. Trying do do trading strategies that beat the market is one of the few things that really is a zero-sum game. In the absence of independent scientific interest to optimizing these strategies, what's the point? You might as well study how to optimize strategies for ultimate frisbee or something.
It's probably best understood as either job audition, fund-raising, or mathematical entertainment.
Sure, I find mathematical finance absolutely fascinating. I just don't think it's worth putting a lot of research energy into. It's usually the boring stuff that matters.
Why do you think it's a weird subject of study, but games like Chess, Go, and Starcraft are not considered weird? Aren't both studied for purely their benchmark potential as opposed to the problem itself? Why are games widely accepted, but trading is "weird"?
Sometimes you come up with a strategy but you don't have bankroll or infrastructures to execute it. It might help you get a job. Maybe the strategy works for a short time. If someone wants to pay you 400k to write algorithms that might be better option.
Because they're academics who choose to forego money in order to advance their career in academia. They could also generally double their income overnight by choosing to move to industry. Many do, most choose not to.