It seems more like a bug than realism to me.

your talk about realism holds true in the scenario of knights vs spearmen.

Now consider another scenario, and one that happens much (MUCH) more often, at least when I play:

spearmen unit goodguys is tying up spearmen unit badguys. The goodguys knights are to storm in from the flank and break enemy formation.

In such a situation, a orderly charge wouldnt have to be set up. 2 knights could do it alone more or less (without it being suicide).

But alas, no. They stroll around and stare.

it's bugged, and has nothing to do with realism.