Simply put: why do Muisca Settlement’s not heal damaged allied units in range? It’s not a very fast heal going from 1 hp per 12 seconds in Dark Age to 1 hp per 6 seconds in Feudal to 1 hp per 4 seconds in Castle.
I don’t think it would see much use but it would be nice for allied Scout cav during Dark and Feudal to get back a couple of hp during the scout fight phase of a game, especially since every scout other than the Champi gets an automatic stat boost when they age up and the Champi fall behind quite easily even if nothing else gets upgraded.