Why?

Simply to assert their self-assigned rights over everything that you write, think and do and to line up ready to easily collect the drip feed of cash they want from everyone.

For this they trade you semi-functional software, vague promises that are usually broken and marketing hype.

That's how all "ecosystems" work.

Which is why I'm not in one for my personal stuff. At work however, they're lining up like good cows for the next milking. They've forgotten that SQL 2014 cost and the Azure price rise already...