As part of the relicensing ZeroMQ did a few years ago, they sought permission from all previous contributors (yes, it was a multi-year effort). Code contributions that they weren’t able to get permission to relicense resulting in the corresponding lines being removed (or functionality rewritten from scratch).
Finally, how exactly do people think corporations rewrite portions of code that were contributed before re-licensing under a private license? It is ABSOLUTELY possible to rewrite code and relicense it.
Edit: Further, so these people think you contribute to a project, that project is beholden to your contribution permanently and it can never be excised? That seems like it would blatantly violate their original persons rights to exercise their own control of the code without those contributions, which is exactly the purpose of a rewrite.