Will’s Empathy Might Something Else.
The capacity to empathize, especially when it shows up as mirroring (which Will does and it’s confirmed on the scripts), can stem from a defense mechanism rooted in the fear of rejection or abandonment. Empathy might not necessarily be about “feeling with” the other in a pure sense, but rather about detecting, and adapting to, and mimicking others in order to remain safe, accepted, or invisible. It’s not conscious, and it’s not manipulative, it’s a form of survival intelligence, hence why in the script he seems to do it mostly (not always) accidentally.