Birds, like all living creatures, have had to adapt to all sorts of challenges. If (since) there is variation in capacity to avoid moving objects, the best at it will survive preferentially. After several generations, only the weakest and oldest will be hit be the rotating blades. Tht evolution in action.
Furthermore, earning, which birds have the capacity to do (despite their brain size :-) ) will inform bird who have close calls. -- and possibly fellow birds that witness said close calls.