The fact that the character has been pining over women, dating numerous women, and nervous around women because he's shy since 1963. No Marvel revamp or universe reset has undone this fact. Being awkward around women has been an integrated part of who Peter Parker is this entire time. Now, is there a problem if Peter Parker WERE gay? No... absolutely not. But if after all this time of establishing the character has having had deep, complicated and long term relationships with ladies you suddenly have him come out of the closet like "Nope! I was gay all along!", it's not only poor and shitty writing for the sake of inclusivity of a portion of fans, it's quite honestly just flat out insulting to gay people.
I have a couple of gay friends who are die hard comic fans (one of which ran a comic book shop) and both of them were completely befuddled by Marvel suddenly flipped a 180 and make Ice Man gay in the comics. It came pretty much out of left field, was contrary to who his character was, and both of them felt this was pandering on Marvel's part.
Want to make a character gay? Completely fine. Make a character who has either been gay from the beginning, or has struggled with his sexual identity, or has not had a long stream of pre-existing complex & deep relationships that run contrary to that idea. Gay people don't need straight people making established characters gay to make them feel good. They need representation that matters. Suddenly changing an character against his established type isn't the way to do it.