@isekaijin - Excuse me? I'm not even an SAO fan, but that's a ridiculous statement to make. These shit level stories have existed LONG before SAO was even conceptualized. You act as if Japan out of nowhere made bad genre's and cliche's in their stories and attribute most of that to SAO in regards to Isekai? Hating SAO has it's limits, lmfao.
There a lot of actual reasons, but I personally think the biggest blame can be attributed to Web Novels and supply and demand. Web Novels allowed every trash tier author to get their stores told and unfortunately, they got popular. Now we're stuck in an era where as long as it's popular and easy to produce, it gets made for quick cash.
Even generic ecchi rom-com's made back in the early and mid-2000s are better than 90% of isekai's that are produced. That doesn't mean SAO is the biggest, or even a real relevent reason why isekai's are bad.
Edit: Also, SAO's ONE good thing about it was it's world building. If these author's were taking notes from SAO on how to create their world, they not only failed, they failed miserably.