Don't Be Afraid To Leave

Let's be honest, burnout is real. Most people want new shiny adventures, sometimes because the idea of running one is more interesting and exciting than the adventure itself. This leads to disappointment and to the emergence of a low level hell from where characters can't get out.

The adventure starts, new characters are rolled, some hexes and rooms are explored, and then people get bored of the dungeon and stop playing for a month or so until the DM takes out his new adventure. But it doesn't have to be like that! There's an untold idea among many players that forces them to commit to whatever they're doing until they don't want to do it anymore. They want to reach the eastern wall of the Barrowmaze or the last floor of the Undermountain and will not stop until they're done (or, more likely, bored) but it doesn't have to be like that!

Just because you're playing Stonehell doesn't mean you have to get to level solely inside it. There's no reason not to have the Barrowmaze or whatever homebrew dungeon you have a couple of miles from the players' starting town. Let them go out, encourage them to do so if they want, let them use their PCs and explore the world. Here's a map I made for my games that kinda embraces this idea (sorry for the awful quality).

Don't be afraid to leave, after all the important part of the game is to get treasures and have fun, and you can do it anywhere!