They're largely private colleges, predominant in Ontario, that have partnered with publicly regulated institutions and have thus been able to access and leverage postgraduate work permits. Those institutions, as you have seen, are largely less regulated than public colleges and universities.
They are the ones that have, in part, been responsible for some of the inequitable growth in the issuance of visas and postgraduate work permits, so there was no longer any reason to issue postgraduate work permits to those institutions.