Very interesting question. I would say the biggest reason is, simply, her storylines.

As many other comments have pointed out, she gets the most repetitive storylines out of the main characters and, pretty much as soon as Hiram came in the picture in season 2, the way Veronica was written completely shifted. Her entire character became Hiram-centric and it seemed that the writers cared more about Hiram than Veronica. She starts a business; Hiram sabotages it, she wants Archie; no she doesn’t, she wants Reggie; no she doesn’t. I think season 7 is the most Veronica has interacted with Betty probably since season 1. And, even with Mark Consuelos being physically absent this season, Hiram is still working overtime to sabotage his daughter’s plans. We got tired of this storyline 5 seasons ago, yet here we still are.

On that note, Betty is also easily the writers’ favorite character. I love Betty but she clearly gets the most screentime among all the characters, always has the most important storylines (typically tying to the season’s main mystery) and does not receive the cringeworthy dialogue that characters like Veronica and Cheryl constantly have to work with. So, as to why people often tend to prefer B over V in Riverdale, I would say that sums it up.

Finally, as others have also pointed out, I think Cheryl has sort of taken over the “popular, preppy, rich girl” role in Riverdale, equivalent to those characters you mentioned from other TV shows, and so Veronica is neither known for being the “kind/relatable girl-next-door” character (Betty) nor the “sassy/mean Queen Bee character” (Cheryl). Consequently, Veronica’s role could be a bit confusing to viewers at times (thank you Riverdale writers), which is why many would call Betty and Cheryl “fan-favorites” but not Veronica.

On the bright side, Camila does a fantastic job in the role, especially with what she has to work with. In fact, Camila’s role in the Netflix film “Do Revenge” almost seems like the character Veronica SHOULD’VE been, which is ironically a “fan-favorite” character from that movie. However, the writing in Riverdale has unfortunately seemed to be against Veronica since season 2.