I think it’s a fairly transparent political move too - this is happening with the background of an ongoing investigation of these companies by congress.

Trump is a political leader, not a musical celebrity. Any moves that hinder his or his supporters speech (he had an account on Parler) is by default a political one, even if at the same time it is a "PR/business reputation move". In this case its big tech wanting to appease the new king on the hill.