For Hummingbird, it's actually possible to get more users, just be little more like MAL.
The information of Hummingbird is so barren that most of the time the voice actor list isn't even complete. You can't browse through studios, voice actors. You can't view staff, how many people have watched the anime, the episode list, the opening and ending songs, similar anime, forum discussions about that particular anime. Like you can in MAL.
I mean, compare the amount of information on these two anime:
I for sure don't search information about anime on Hummingbird. I go on MyAnimeList.
And for the Manga section on Hummingbird. Holy shit, if that isn't absolute garbage.
There are no reviews, most of the time there isn't even any information about the particular manga. I mean, compare these two.
If Hummingbird wants to attract more users, they should start working on these kind of things.
There's is not much reason to actually use Hummingbird. MAL is a better alternative, if you don't mind a big community where you can't voice opinions without getting scolded.