Why shouldn't a precooked pie be frozen? I bought a Selection brand strawberry pre-cooked pie. I just read the instructions on the pie and just realized it was pre-cooked but it says to not freeze the pie. Unfortunately, I froze it right away when I got home because I couldn't find my reading glasses and didn't read the instructions.

Are any health concerns here? If not, what could the reason be for being warned not to freeze the pie?
Generally, these warnings are for food quality reasons, not for safety reasons. 

Assuming this is a fresh strawberry pie, I'd guess that - because strawberries don't bake or freeze particularly well - if you freeze the pie, the fresh strawberries will turn to mush and not taste very good, particularly if you try to bake it to heat it up.

Freezing something should never make it unsafe to consume... freezing is a preserving method.