Back in the day, terminal emulators were fast enough that they were up to date by the time each 50Hz/60Hz period came around - why on earth are they now so much

Back in the day, terminal emulators were fast enough that they were up to date by the time each 50Hz/60Hz period came around - why on earth are they now so much slower? A couple of days ago I spent a while trying to figure out why a piece of hardware appeared to be outputting serial data in bursts. After eliminating issues with the underlying hardware and buffering in the USB stack, it (too slowly) dawned on me that the issue was entirely due to how slow terminal emulators have become (this was on a fastish PC). Updating a screenful of text at 60/120Hz, why/how is it so much slower these days? (and what benefits have we gained in return for the slowdown?).