'Placeras' simply means 'from the plaza': the name comes from the squares and markets where they have always been sold.
Tortillas dipped in guajillo chile sauce and fried, folded around cheese and onion and served with potatoes, carrots and often chicken, from market stalls and antojito counters.
Why it's made this way: They are Morelia's signature antojito, still sold at the stalls of the Mercado de antojitos de San Agustín in the historic centre, where the city also holds an enchilada and corunda festival.