IIRC, Firefox Send shutdown because it was getting abused - I see you need an account to use Bitwarden Send, which I imagine helps mitigate against that, but it's also a barrier to use. Would be interesting to know what other anti-abuse mechanisms are in place.
Bitwarden Send is a feature add for existing users. It solves a very real problem of sharing passwords (and other sensitive information) with others.
Before Send, the way Bitwarden recommended sharing data was by creating a group account of some sort (family, business), and using a shared collection.
