Because the OSI has been defining and stewarding open source for 25 years. It is the de facto definition and has been recognised as such by multiple governments around the world. Anyone trying to muddy the waters is probably trying to sell you their “source available” software as open source.
Most organisations and individuals that disagree with their definition are trying to sell you source available software as open source.
If it’s not OSI approved then it’s not open source. I hate it when companies try to dilute the open source moniker. This is “source available”
I think that vulnerability was a non-issue. Someone could get to your password if they had full access to your machine to run arbitrairy code. But if someone has that much access, it’s already game over.
But yeah, Bitwarden is better IMHO
Why wait? Switch to Firefox now
RMS doesn’t disagree with OSI about the open source definition. He just thinks his Free Software definition is better. But RMS would most certainly not call “source available” software “open source”