Contributing to that perfect storm is that FiM was one of the first notable examples of a girl-oriented show having a budget and being well made. Creator Lauren Faust lamented that her girly childhood interests always felt neglected by producers and companies in her childhood and she resolved to create something with more depth and cogency.

Setting up the success of MLP was Powerpuff Girls a few years eariler, which took very feminine protags and put them into traditionally masculine roles, which got a lot of male fans onboard with feminine aesthetics and themes.

And going back further from there, the entire magical girl genre got popular Sailor Moon, which was marketed as shounen (boys) anime (despite being a shoujo - girls - manga first) - a trend that was carried forward into today. While that designation was not shared or understood by western audiences, it was nonetheless recognized by people who worked in and followed animation closely