Why not? They get someone else on the hook for the rent and tenancy obligations and it’s not like if they get rid of the prime tenant they can drastically increase the rent if it is a rent stabilized apartment. They’d either have to spend $$$ litigating the successor’s claim or time and $$ finding a new tenant who would be sbj to the same RGB increases anyway.

Again, it would not matter if the LL rejected the request to add the relative because it is the successor’s burden to prove they asked. If they cannot meet that extremely low bar, set by statute, then maybe they are the ones full of shit.