The ride through Low-level is always fun, as long as there's the possibility of making your way to moderate and high level play.
Low level (1-7ish) is fun because everything is dangerous. Everything is 'new'. New character to play/explore, new people to meet, new environment to explore, new plots to hatch or be swept up in. You're a small fish in a large pond. Everything is 'difficult': not very skilled, not wealthy, not connected, not powerful.
But I think there's a lot of progression-satisfaction at work as well, as you can gain levels rather quickly for a while. So your options continually expand as your skills and spells (and possibly material goods) blossom and grow. It's the 'build-up' phase and the journey can set up all sorts of play in the later levels.
Moderate level is just low-level but everything is on the table heh.
Small sample-size but it seems high-level stuff is less popular (decreased focus on progression?) and looked on as difficult to facilitate. Maybe it requires a bit of a shift in thinking from both the players and GM but it doesn't help that so many RPG products imply or straight up say that higher level PCs are difficult. Shouldn't be. The 'characters are too powerful' trope never cut it with me.
Nearly every fantasy book written is about 'high/extreme-level' people, and they have all sorts of difficulties and goals and adventures etc.
-Elric of Melnibone- Master Sorceror of his age, Compacts with Elemental-rulers, has the ear of Arioch, and wields the most powerful artifact in the multiverse.
-The Black Company- High end mage-types (The Ten Who Were Taken), powerful warriors and just as deadly enemies/plots.
-Vlad Taltos series- Virtually every characters is extreme-level, master sorcerors, warriors, and assassins wieding sould-destroying artifacts. Add in some gods and alien threats for flavour. Doesn't lack for adventures ranging from mundane criminality to political shenanigans to epic magic threats.
-Malazan Book of the Fallen- 10 books featuring everything from demi-gods, teleporting mage-assassins, long-thought dead ancient races of terrible power, individual duels to massive battles involving magic rituals and demons, interesting cultures, continent hopping, among much more.
All sorts of gaming possibilities open up with higher levels. Unless one really dislikes such play there shouldn't really be any problem coming up with activities and obstacles.