Regardless of the legality of a thing, the foundation might of course recommend against using it. Imagine that someone wrote a shitty book (without stealing any content) which ends up as the only result on Amazon. It’s perfectly legal to release such a book and it would be sensible for the foundation to warn the Zig community about the lacking quality.

Just because the license allows anyone to fork it and sell it doesn’t mean that Zig is obliged to endorse it.