In general, I think high level play requires a level of investment from the players (including the DM), that is more than what the casual D&D player enjoys. For one, I think successful high level play almost always stems from progressing through many levels before it (ie starting no higher than level 5) wich of course requires time. That alone can prevent high level play. Since 2014, I've had 2 campaigns that went from 1 or 3 to 20, and four others that started below 5 but petered out around 12-14 due to the group falling apart for various real life reasons. Now, I do think you can have a successful high level campaign that starts high (see BLeeMs EXU Downfall for a good example), but that requires players with a strong mastery of D&D and a lot of trust in setting up the scenario. But even in that case, the 'campaign' only lasted 20 hours or so.