Capitalists aren’t very interested in building commons; it’s not their goal. They can use both copyleft and permissively-licensed stuff to accomplish their goal.

If your goal is to build a commons that capitalists can’t use, then you’re looking at copyfarleft. Being able to bootstrap that effort with already-existing code is very helpful. You can do that with permissively licensed code, but you can’t do it with copyleft code.

Or to put it another way: if you wanted a copyfarleft kernel, you could start by forking openbsd, but you couldn’t start by forking linux.