I think the problem is how it was communicated. There were mainstream articles with headlines like “It’s time black and brown people were on the pride flag.” It makes it sound like PoC hijacking pride to push their agenda. Sort of like, “this is all about us and our movement now.” But that’s not at all what the progress flag is about, at all.
The progress flag represents the forward momentum of inclusion and progression. Without opening a big can of worms, there’s lots of racism and bigotry even within the LGBTQ community. PoC, trans people, queer, and bi people are fetishized, ignored, stigmatized, excluded. There is this gross pecking order within the LGBTQ community, and the majority can be really trash to the minority. The progress flag says, “these people are welcome, too,” and reaffirms that the work is toward acceptance of everyone, not just gay white men.