Bella isn't the most popular LI because she gets the most screentime, she's the most popular because the ,,enemies to lovers" cliche is probably the #1 trope in storytelling that gets people invested in a relationship, primarily because, these types of relationships are so fulfilling when 2 people who hated or strongly disliked each other start to appreciate, care and like each other more because of some similarities that they have and the difficulties they go through together.
On the other side of things, characters like mila, vic, nia, robin, sonya and even nami to some extent, won't reach bellas level of popularity, because they already started by either liking nika or just being on friendly terms with him, which is fine, but not very interesting.
This is also the reason why Zara and Sasha are starting to get more fans and why they''ll probably be #2 and #3 most popular girls soon.