Probably because either:
a) Not many people were aware they existed
b) They were heavily guarded or hidden, but the destruction revealed them in plain sight
c) No-one had researched how to use them, unlike Orochimaru.
I'm pretty sure most people would have left them alone out of pure respect. It's considered quite rude to take something from a temple in Japanese culture.
Aside from that, anyone who even tried to use a mask would probably become possessed or killed in the process. They might even lack the ability to activate them.