I'm probably an outlier, but my 5E campaigns so far have went from 3-20, 3-16, and 3-12 (and I wanted to run this one a bit longer than I did). Until recently I was also in a gaming group with a DM who ran high-level one-shots several times a year, including a 20th-level party that fought Orcus and a horde of undead, a 20th-level party that fought Tiamat, Vlaakith, and Asmodeus, and a 16th-level PVP event.
As for why higher-level play isn't more popular, perhaps the average player finds the number of options available at those levels overwhelming to keep track of? I personally use a custom character sheet formatted like a monster stat block to keep track of my PC's traits, actions, bonus actions, and reactions, and I make cheat sheets to keep track of my most commonly used abilities. Most people probably use a more standard character sheet and no cheat sheets, I'd assume.