Hmm, as someone who teaches intermediate microeconomic theory, I'm super interested in this as it impacts my daily work.

Micro theory is interesting in that to do it well you actually need to be good at both... solving complex algebraic problems, while at the same time converting a verbal scenario into the relevant mathematical equations. I think that's what makes it hard for students. Being good at one (abstract math or word problems) isn't enough. You have to be good at both.