I’m guessing it’s because they don’t want to spend money on someone who can translate well, instead opting for they guy they already have who says, “I know some English!”
I read somewhere that the poor grammar and spelling is a deliberate filtering method. The theory is, the scammers don’t want to waste their time trying to string along the less credulous who might back out at a later stage. So, they deliberately fill their ads with a bunch of groaners. The people who respond are more likely suckers.
It is my gladness to be renting the apartment to you of which you have shown interest in.
I am Jack’s suspension of belief.