Sixel support unfortunately came to terminals in 01988, as that page explains. I saw it myself in 01992. Sending uncompressed color raster data over a 9600-baud serial link again every time you wanted to look at it was a terrible idea, made worse by the stupid Sixel encoding inflating it by an additional 33%.

Today, when we're sending it to terminal emulators running on teraflops supercomputers over gigabit-per-second links, it's only a waste of CPU and software complexity instead of user time and precious bandwidth. But it's still a waste.

Why couldn't we have FTP and Gopher support in web browsers instead?