But the thing is...
...the main character is usually not the most popular one.
This isn't universal, but in a lot of stories -- especially Western fiction -- the lead character is generally somewhat watered down and more relatable compared to a more colorful supporting cast. Reason for this is that if you go too hard on a personality that people don't enjoy, and that's the character you'll be dominantly following through the entire series, a lot of people will decide that's not the kind of person they want to be spending their time with.
I don't watch The Owl House so my comments are pretty broad on this, but Luz is a regular girl from our world who gets transported to a fantastical magical land, right? That premise means that we as an audience know a lot more about her because most of us are also regular human beings from the real world and have a reasonable baseline assumption about her background and life experience. This is compared to the Boiling Isles, which is filled with magic and intrigue that Luz -- and the audience -- are all working to understand, both in terms of the literal magic an the world itself and in terms of other characters. A character like Amity is inherently more interesting than Luz because she's an unknown and people want to learn about her.
To invoke the Series that Must Not be Named, for instance, relatively few people pick Harry as their favorite character. Nobody hates him (except maybe in Book 5, where his untreated PTSD turns him into Capslock Harry and he gets a bit hard to deal with for a while), but usually fans will be more interested in Hermione or Ron or Luna or Draco Malfoy, or maybe even Dumbledore or McGonagall, or Lupin, or Tonks... Harry is pretty milquetoast compared to his more exaggerated, wackier wizard acquaintances explicitly because they're more exaggerated and wackier.
A little more in Lily's field, how about Gravity Falls? People like Mabel and Dipper, but they LOVE Grunkle Stan and Soos and Blendin Blandin and Bill Cipher and Pacifa and... you get the idea. Soos in particular if of Latin descent and memed as the Perfect Man in the fandom. What racists.
And of course, directly in her wheelhouse:
This.
It's just typical of how the characters are handled. Usually the lead is the most down-to-earth and relatable, making it easy to like them but less common to love them. There's no great white conspiracy.
