From a business standpoint, not doing so is just leaving money on the table at this point. Nintendo has already shown they don't care about integrity or making the best game they can with this franchise, and the consumers have already shown they'll buy the games no matter what, so what's stopping them? Of course from a consumer standpoint, we shouldn't want them to make the games even worse, but that's from a linear perspective.
The way I see it, by making this bad game even worse, the additional cash flow can be used to make Nintendo's better games even better. Imagine if Fire Emblem Three Houses had a bit more money put it into it, it probably wouldn't look almost as bad as Sw/Sh lul. Basically, if Pokemon is going to be Nintendo's black sheep, they may as well take full advantage of it.