Blocking individual accounts is something Parler can do (and chose not to), not Amazon/Facebook/Google who don't have access to the contents of those accounts (at least not easily).
Also, it's worth looking at some of the hacked info that was released - Parler had a serious moderation system, but it was used to make sure people had MAGA viewpoints, not to prevent violence. This is not some free and open platform, it was a controlled one that purposely built an echo chamber of violent rhetoric. Twitter and Facebook don't allow the same kind of violent rhetoric, lies, etc., and while they may not do an ideal (or even good) job at it, the fact is they're broad platforms used for a whole lot of things for a whole lot of people and are absolutely not comparable to Parler.
I can remember very well calls for violence in twitter against Nick Sandemann. And I remember very well those calls for violence not being removed at all.
Also, during the riots of 2020, it was extremely common to find calls to violence in twitter that weren't deleted.
What's your point, that they apply TOS inconsistently? I don't think anyone will disagree with that assessment. They let Trump violate the TOS for 4 years.
They are perfectly within their rights as a private business to make those exceptions. Is it fair? No. Would we much rather they apply things consistently? Yes.
The question is, do we want to enforce who and what they can and cannot allow on their platform via law, or do we want private businesses to control who they are allowed to do business with?
Also, it's worth looking at some of the hacked info that was released - Parler had a serious moderation system, but it was used to make sure people had MAGA viewpoints, not to prevent violence. This is not some free and open platform, it was a controlled one that purposely built an echo chamber of violent rhetoric. Twitter and Facebook don't allow the same kind of violent rhetoric, lies, etc., and while they may not do an ideal (or even good) job at it, the fact is they're broad platforms used for a whole lot of things for a whole lot of people and are absolutely not comparable to Parler.