Look at all the long lived open source software around, be it Linux itself, gcc or KDE. They all have gone to great lengths to preserve all commit history across all migrations of VCS or code hosting.

(Sometimes absurdly so, as in the case of gcc, where flamewars have been fought to preserve commits that were broken to begin with.)

That is important, and that much care for the code probably helped them survive for so long. Botched VCS migrations is not something that should be accepted anywhere.