Regarding your question about French, I'm not too sure. There/their/they're would be la/leur/ils sont, so perhaps there's scope for the first two to become conflated, not so much the last.

As far as I know the biggest issue French is facing is the injection of English words where there isn't a French equivalent.

Then again, French people seem to absolutely loathe the version of French spoken in Quebec so there could be a plethora of other issues involved that we don't have in English.

Regarding your second point, personally I'm not sure but ignorance certainly plays its part one way or another.