- External fonts are often purely cosmetic. Using what over time adds up to several megabytes of data for cosmetics is inconsiderate.
- inb4 "just disable remote fonts if you hate them": doing so breaks many websites that use icon fonts. Expecting users to have to manually configure 50+ websites (yes I did this, I count 54 websites on my exception list) is just insane.
- Many people need to use local fonts. Some dyslexic people actively choose a font that helps them read more easily. Asking someone to play the whack-a-mole game of "will disabling remote fonts break this site's icons or not" game on every site because of a disability just isn't right.
Just use sans, serif, and monospace for content. Let the user agent decide what that looks like, not your company's branding.