Because you are the product, not the client. You are only catered to enough so that you may be coralled. You are basically cattle to these corporations.
As for why this is happening now:
The economy is in a downswing right now so we are going to see cost cutting and belt tightening.
Entrenched proprietary social media platforms are basically monopolies. You cannot choose to use an alternative because these are walled gardens and leaving means losing your ability to communicate with large groups of people. The larger and more entrenched these big firms get, coupled with lack of regulation means they can do whatever the fuck they want. You have no power and no choice (except for the Fediverse, a one-time pain to migrate to).