People are also more aware of plastics in their food and using plastic tupperware in the microwave might add a large amount of plastic to the food [1]. Due to this I also switched to glass containers, which are also easier to clean.
Wish my neighbours and relatives would listen - tell them that and they are quick to pick one of those plastic containers, flip it, and point to the text at the bottom that says "Microwave Safe". (And I am talking about no-name, cheap brands that are probably from China).