>>213502715
Sometimes it's not obvious a movie is shit until it's nearly finished. At that point, it usually will make slightly more money than the cost of finishing the movie so you might as well finish it. Also, you never know. Maybe it'll be popular despite being shit or become a cult classic because it's shit.
Your OP is a good example. Master of Disguise sucks, but there's a lot of people that love it, even if it's ironically. People still talk about it even though it's 25 years old. It has probably recouped its budget by now. If they just shut down before finishing, then its legacy and all the money spent making it would be lost with nothing to show for it.
