Why do missile units always run?

I hear everyone talk about how OP missile units are but even when I have a strong front line they end up turning and running. Yes I put them in guard mode sometimes and it still happens. Especially with gunpowder units where I have to do a checkerboard pattern to get LOS. Any tips from you guys? Edit: I’m a retard. Over 700 hours in this game and never knew to turn off skirmish mode. Pretty wild