Because our "leaders" are not smart enough to understand this, they've just been told it's bad.

Because they want to pretend it's ok to have zero encryption and that's much harder if facebook and others say it's not.

Because passing an actual law to actually ban it would take effort and they're lazy

Because there is a non-zero chance they can't really ban it, at least not without banning a lot of other things like e-commerce and online banking, so a gentlemans' agreement to keep 95% vulnerable is much more manageable.

Because in at least some of the jurisdictions it might not be legal ("constitutional" in the US, "in accordance with the European convention on human rights" in the UK etc) to force these things by law.