It seems like they just wanted to play dress up.
The dimensions of combat in the days of musketry aren't quite the same as the ones of today. Plus, one must not overlook the role of fashion. u/StoryWonker and u/dandan_noodles explain further in this thread, and u/PartyMoses has a practical look at the uniforms. As always, should anyone have more insight to contribute, further posts are always welcome!