In Shogun and MTW, this sort of tactical retreat was much more common than in RTW.

Often a weaker enemy would apparently decide to fight but on the battlefield, looking at your battle hardened & notorious killers, the army would decide that suddenly they realised they had better things to do elsewhere...
A couple of notable instances I experienced include a near full stack defending army running from my 16 Kensai attack force and a particular instance of my well outnumbered and outclassed army steadfastly staying in formation within a forest clump while the Mongol horde probed the middle, both flanks (about 150 losses to the Mongols, 60 or so to me), then withdrew realising that they couldn't beat me in the trees & I wasn't going to be lured out either.

It still happens in RTW but much less often :(