I've had 2 1-20 campaigns in 5e (never had one in previous editions).
The first was in a completely homebrewed world, played in person with 3 players, and took about 4 years, but only about 70 sessions, each session lasting 5-6 hours. It started in the playtest, and we played when we could, sometimes taking breaks as long as 10 months.
The second started shortly after pandemic lock-downs, played on Roll20 with 5 players, and took 2 years and around 90 4 hour sessions. It began with the free Wildemount module, then continued using EGtW as a guide.
In both cases, I think the longevity of the campaigns came from three major factors.
The first, and most important, was each group. 2 of the original 3 went on to the second campaign, and in both, the level of trust and support between everyone was tremendous. It was luck both times that brought us together, but it was work by everyone to keep it going for so long.
The second, I believe, is that I never planned for more than the current Tier the PCs were in. This allowed the campaign to evolve based on the choices of not just me, but the PCs and the random luck of the dice. I could never have predicted the end of either game at the beginning. The story told in both was truly a collaborative effort between Fate (DM), Choice (PCs) and Chance (dice).
Finally, I believe 5e itself is responsible. I'd count 5 of the 6 players between the two campaigns as 'casual' D&D fans, and everyone had busy lives and responsibilities. But 5e is designed in a way that casual players can come in and have a great time even if they are not hard core gamers. Mistakes can be made in combat without things falling apart. And the rules can be left behind for a weird encounter or adventure to do something completely outside of the framework, and then snap back later. The game can flow between skill checks, TOM and grid based battle in a single encounter based on what is appropriate for the moment. It can leave dice rolls behind for hours at a time and still pull on the lore to guide the story. It encourages bold experimentation, knowing that you can always go back to the framework if you need.