I mean, Makoto IS best girl after all ;) I can imagine her actually being quite popular in school but all the girls (and guys) being way too intimidated to actually speak to her :P
^I think that's the way they show their affection.
Kita show hers openly, showering Bocchi with a little of her affection constantly.
Bocchi hide hers, accumulating her affection into one big heart and only show it to Kita when the time is right.