I’ve only been interested in Aquaman during the One Year Later ‘Sword of Atlantis’ run, so I may not be the best opinion on this…
There’s a lot of superheroes out there.
And a lot more that don’t have their own books that very likely should.
I believe that current trends are showing more interest in non-superhero comics.
I personally think this is because fans are getting better superhero content outside of comics.
The tv shows and movies are plentiful and tend to be much better than the comics, which aren’t only expensive and padded to fill trades, but are almost always devolving into a meta-fiction plot that routinely reboots or recycles everything, undermining the foundation that the stories are built on.
A lot of people just want good stories.
Stories that aren’t artificially inflated to fit into collections or compromised to accommodate the latest multiverse-wiping event.
Edited to add:
Love it or hate it, Momoa’s turn as Aquaman has boosted the character’s popularity back up to, or even above, where it was at during his Saturday Morning cartoon run in the '60s.
It’s pretty much guaranteed that he’ll be getting a regular book again.