Basically Nintendo always had bad blood with PM because the mod defied Sakurai's vision of what Smash stood for and should be. PM came out a few years after Brawl, and Everyone in the Melee scene loved at least the idea of it. It was like Melee part 2 to them.

PM gradually grew as It appeared at essentially every single Melee tournament, and almost all top Melee players would play and everyone generally liked it. Infact, for a while, PM was bigger than Melee.

As the scene grew, however, Nintendo, namely Sakurai, was unhappy with scene. Gimr, now running VGBC as more of a business, saw this as a threat to what he was doing. Gimr seemingly out of the blue announced that PM would no longer be streamed on VGBC.

This discontinuation of PM on VGBC and at Xanadu Lead to the scene declining as less viewers went out of their way to go to ProjectMCentral. This went even further when Gimr chose to remain silent regarding Project M vods he took down from his Twitch channel. As time went on, PM faced even more hardships as it was soon 'banned' from being streamed on Twitch, as well as Nintendo banning it from any tourney it sponsored.

What basically happened was the scene looked for a scapegoat for PM viewer numbers and tourney sizes declining. The community found blaming Gimr easy, as he brought PM to fame initially, and was seen as the only one who was able to keep PM on par with/above Melee viewership and tournaments. His continued silence on the PM vods and his in general silence when talking about PM made him a target.

Today though, most people have moved on from Gimr and have (at least somewhat) forgiven him for his decisions. Gimr resolved the vod debacle, and as Nintendo partners with even more tourneys and banning PM, People have generally let Gimr hate turn into a meme.