Also, at least for Apple, I recall them giving Parler an ultimatum to moderate their platform. For example, if an app was full of child porn or ISIS videos, I would imagine Apple would take the app down. Similarly here, due to the lack of moderation, Parler was full of doxxing, call to violence and recruitment and planning for attacks on the Capitol (both the one that happened and future ones).

That's the reason for why it was removed, not simply because Apple doesn't like conservatives as they will claim.