Let's just call it "composting." Something flowers and blooms into a beautiful experience, draws a critical mass of users, which draws the attention of parasites, the flower withers, dies, and turns to crap... compost.
The composting of the internet.
But composting implies something good is coming to replace it.
Not just possible, inevitable. It's why we should demand more interoperability - so platforms have to compete with each other instead of milking a captive audience.
I think it's become inherent to Internet platforms. The playbook is too well-known for founders to ignore.