I always thought it was because it was used by people who thought it made their poorly written crap seem more personal and human, when in reality all they were doing was one exceptionally low-effort action: pick the one wacky font that shipped by default with Windows. But instead of making their writing actually seem more personal or human, it just made it look cheap and unprofessional because it was equally associated with the sort of output you'd expect from any child playing with a 1990s-era Windows computer.

(The right answer is instead to embed personality and humanity into the words themselves, which is comparatively much higher effort and indeed beyond the skill of many people.)

Over time we've grown accustomed to working within pre-packaged emotional bounds (e.g. the limited set of emojis) and the meme-status of the font has long since passed so it would probably not be quite the same faux pas today as it was two decades ago.