Why don't apps / sites uses emojis instead of icons?

A lot of software still doesn't handle unicode well. Classic example being anything parsing SSIDs from Wireless access points.

I wanted to name my network five bleading hearts or "JEFFREY EPSTEIN SUICIDE SQUAD", but I had to settle for "EPSTEIN SUICIDE SQUAD" due to unicode issues + character limits.

I previously used the network name "FLESHLIGHT" about a decade ago in college, but I was told such a name might offend the neighbors so I picked a different one when I moved back.

TL;DR: The issue isn't bandwidth.