A lot of open source stuff is libraries and utilities though that is pretty entrenched in the code. It is hard to even find out about a violation, let alone prove anything.
Imagine I came up with a new algorithm to do Fourier Transforms 10% faster than FFTW (or whatever the current market leader is) and make a library and I release it as GPL. A company could fairly easily just import it to whatever project they’re doing, and it would be extremely difficult for me to prove anything, especially if I don’t have any obvious things like strings in there.
That’s not even taking into account that it would be relatively easy for a corporation to just pay a junior engineer to do a direct “port” of the library to another language and pretending it’s their own independent work.