Already posted a rebuttal of this. It's a simple matter, Peter being single does not serve the stories like it did to prior to the development of MJ in the franchise. Given Spider-Man fans know and recognize Peter and MJ as the OTP for the Spider-Man franchise, having them exist in those roles in story would better serve the stories for readers. Trying to pair Peter with other women is not effective as it used to be prior to this. It isn't actually working for the stories, because it doesn't work for the characters that fans know them as.
It's to the point that seeing Peter date other women than MJ feels out of character, because it is, since we are all certain he belongs with MJ, their love has become one of the pillars the franchise is built on.
Cogsigned.