Note that copyright holders for an open source project is often a very long list of people that would all need to approve of having their contribution relicense

Note that copyright holders for an open source project is often a very long list of people that would all need to approve of having their contribution relicensed. It's a bit of a complicated matter. Considering attribution was removed, I doubt it was approved, but it's not impossible that they somehow learnt and decided not to care as enforcement can be unreasonably cumbersome.