I actually think this is representative of one of the best parts of eventing. Everyone can wear whatever they want (though for championship events the men usually try to agree and so do the women to appear united as a team), and they can be as formal or relaxed or “girly” or “manly” or whatever-other-term-people-might-want-to-throw-at-them as they want, and none of it affects their ability to ride their pants (or skirts, as the case may be) off on the field of play.
Tamie Smith jogged up in a purple skirt because she felt like wearing a purple skirt? Sure, but she still threw down a dressage test 10 marks lower than Boyd and left more show jumps up than Oliver, so she wins. Pants, skirts, and whatever is under them be damned - in eventing, you win or lose on merit, and nothing else. I love it, and I’m proud of it.