soggy not crispy

Please explain this to me.

When I take bread from the fridge (cold not frozen) and put it in the microwave for about 20sec, it will warm up, but it will also become soggy and taste like wet paper.

Where does the humidity come from?

However, if I would use the toaster, the same bread would warm up and eventually turn into crispy toasted bread.

What is the difference? Why can I not toast bread with a microwave?

Please, explain this to me with your string theories...