The cynic in me believes the whole Fuchsia thing is to avoid the GPL.
So, they are moving from GPL to a more permissive model. Though, sure, they could easily change the terms for the final version..
[1] https://arstechnica.com/gadgets/2017/05/googles-fuchsia-smar...
Now, it permits proprietary derivstives, but that's a different issue.