: Why do we say: bore pri ha'adama - but: hamotzi lechem min 
ha'aretz? 
: Why not: bore pri ha'aretz, or: hamotzi lechem min ha'adama?

My guess is in two parts:

1) For fruit, the bracha needs to distinguish between fruit of the 
ground, and fruit of trees. "Eretz" is a more generic term, referring 
to the planet as a whole, rather than the dirt as opposed to trees, 
and is therefore unsuitable for this purpose.

2) For bread, the wording is taken from a pasuk: Tehillim 104:14. (If 
you want to know why that pasuk used aretz instead of adamah, fine, 
but that's a different question.)

Akiva Miller