Cancelling Parler isn't about Trump or the riots. Trump will be gone in a few days. These are rationalizations to ban non-leftist platforms.
The left is a totalitarian collectivist movement. In order to establish the dictatorship they desire, they must suppress opposition to achieve full control of society.
Hence, they will attempt to brand anything that rebukes the their fundamental principles as racist and backwards, and worthy of censorship.
Parler was founded by libertarian types who don't support Trump, or consider him anything more than the lesser evil, and who have nothing to do with racism. Yet, the left is branding them right-wing extremists, white nationalists, Trump supporters, "conspiracy theorists," etc.
Give me a break. The left are a bunch of fascist ass hats.