An irreversible migration isn't a bug, nor is anyone saying the answer for any software problem is to not have bugs.

They're saying the solution to the specific problem of being unable to rollback due to irreversible migrations is to not write irreversible migrations, which is a completely valid solution and indeed the correct one. The whole point of migrations is to track db changes so that undoing them is easy.

That misses the point.

Code and the DB always need to be compatible one version forward and back. That's required engineering discipline.