Thoughts
Open Source arises out of free market competition when the framework/library is simpler than the application that builds on it. Because then
it's easier to rebuild the framework/library then it is to rebuild the software that exists on top of it.
If you're building a house and your stone supplier increases prices, what do you do? You find a different, cheaper, supplier. If you're being charged a fair amount for a simple software framework; and then prices increase, what do you do? Well, it's easier to create a compatible clone of the simple framework than it is to migrate your complex application to a different framework.
For this reason, it doesn't make any sense to start a project with a non-free framework because the vendor lock-in is so strong. And similarly if a free framework becomes non-free it makes more sense to fork that it does to migrate.