GPL is the only thing standing between us and Embrace-Extend-Extinguish.
There’s a reason that “Stallman was right” is a meme in the FOSS world.
Do you think IBM wouldn’t make Red Hat completely proprietary if they had the chance? They already tried to use their customer licensing to restrict source access!
It only takes one successful proprietary product to gain mind-share and market-share and become a new de-facto standard, and then all of the original FOSS has to play catch-up and stay compatible to stay relevant.
See Jabber/XMPP for an example.