> WebKit

Sort of an exception that proves the rule. Yes, it's great and was released for free. But at least partially that's not a strategic decision from Apple but just a requirement of the LGPLv2 license[1] under which they received it (as KHTML) originally.

And even then, it was Blink and not WebKit that ended up providing better value to the community.

[1] It does bear pointing out that lots of the new work is dual-licensed as 2-clause BSD also. Though no one is really trying to test a BSD-only WebKit derivative, as the resulting "Here's why this is not a derived work of the software's obvious ancestor" argument would be awfully dicey to try to defend. The Ship of Theseus is not a recognized legal principle, and clean rooms have historically been clean for a reason.