Right. As you would desire and hopefully expect, even if it might be technically possible to squeeze out slightly better compression with some non-free technology, it's very attractive for everybody to agree on the free things instead.

The FSF even offers this as one of the few reasons you wouldn't use Copyleft. It actually would be better for society if everybody copy-pastes the Opus code and refuses to let you see their source code, than for them to use a proprietary codec instead.