Ready to eat food not suitable for microwave
Because it is made from pastry dough. Pastry dough (and any other kind of dough) gets ruined by a microwave. See this question for details of what will probably happen. 

The only exceptions for dough in the microwave is pasta (which is supposed to be boiled in water anyway) and some kinds of very soft batter, which can be eaten immediately as a "microwave cupcake" (I think they get unappetizing if left to stay for a while). Any other kind of dough is destroyed by the water escaping the starch as steam.