As they are free to do. The right tend to be the ones defending the rights of companies to do whatever they want, and it has bit them this time.
Maybe we'll get lucky and find that they were wrong, and that this move causes enough public backlash to give other social networks a chance to thrive (if we're really lucky, maybe even decentralized ones!)
The only information we have is that it was internal pressure too be a "better company."