I truly believe in Mastodon and think it's going to be the next big thing and all the corporate players are here for various reasons, good and ill, because they also believe that.
The one positive is them coming here is a self fulfilling prophecy of Mastodon's rise, because they will bring more users to the platform.
I just truly hope Mastodon's FOSS side will adapt and win out in the end. I think it CAN but I don't know that it WILL