1. hair ruffling is a dick move. the intricately arranged hair touhous have probably takes ages to put together just right. with one ruffle it's ruined. dick move.
2. the humans aside, how the hell do the wilderness-dwelling youkai maintain those fancy dresses? Ribbons and lace don't grow on trees.
3. the incident/resolution system is utter shit when you consider it from a long-term (for Yukari, i.e. over centuries) perspective. at the rate incidents happen and with the sort of power incident-causers generally wield, eventually a Miko is going to fuck up with catastrophic consequences. Especially true since Mikos are human and powers and predispositions waxes and wanes with age.
hair ruffling is a dick move HERETIC. May you burn at the stake.
Touhous come with clothes in varied forms when they are born. The clothing regenerate when they are dirty/ripped/destroyed.
That's why there are so many Youkai, can't really kill them all and soon there will be enough again. Yukari probably made most of the humans sterile so that they won't overpopulate Gensokyo. And Reimu is not human anyway. More like a monster in human form.