What is the purpose of horizontal blocks on a bearing wall?
Can't say for sure why they did it in your situation, without knowing a bit more details. 

Typically blocking is installed to prevent framing members from twisting or warping, and to stiffen and add strength to the wall. Though it's also common to install blocking, where fire stops are required by code. Blocking can also provide an attachment point for cabinets, chair rail, counter tops, etc.  In walls where the studs are spaced further apart, blocking can provide support to the edge of the drywall between studs. 

But again, this is all speculation without knowing more details about your situation.