They probably considered it poetic justice, in a way - a Cardassian, *any* Cardassian, being forced to stay behind while all of his fellows leave. They wanted Garak to feel alone and abandoned.
Now of course the Bajorans didn't openly harass or torture Garak. Just having him be there, alone and (as far as they knew) helpless, was all the revenge they needed.
Plus, as Garak himself said: he's a very good tailor, after all.