I mean it's an extant subgenre sure, but it's a loooooong way from being what "every writer" does, I think you might just have confirmation bias my dude, or maybe like you're specifically seeking out genderswap stories in order to bitch about them?
But hey, lets do a little experiment, there are 42 pages worth of Genderswap stories on Mangadex, with 32 titles to a page that leaves us with approx 1344 genderbend titles overall, of those, only some are gonna be Shonen or otherwise actiony stories, and of that, not all are going to have an OP protag
Now if I look at the "Action" titles, we have 313 pages worth resulting in a total of roughly 10016 action stories.
We all know that each of those are going to have action in them, it's in the name, but even if only half of those Action stories have OP protagonists, that by itself is still almost four times as many OP cis protagonist stories as there are genderbend stories in total
So you are either ignorant or deceptive, pick one.