With Data, however, you don't seem to get the hero worship / role model thing that Janeway (inexplicably to me) appears to generate in her fans. Data was a great character that I miss. I suspect most fans feel similarly, but that's it.
Janeway (and yes, my opinion is coloured by my dislike of Kate Mulgrew as an actor) was badly written,
inconsistent and annoying. I cannot deny that something about her connected with her following, but it almost seems like a mother / sister / mentor relationship her fans project onto the character.
For a large number of Janeway fans being female, by and large it's simply the appeal of a strong, independent, female leader, which in Trek or any other fictional realm or in reality even today are few and far between. These type of role models show young girls a positive influence and that they can achieve great things. Janeway as with other heroes, became a beacon of different things to different people.
It can't be denied that Kate Mulgrew was a path setter by portraying Janeway. She opened many doors for other women in sci fi. I also believe her fans loyalty comes from how she interacts with them and how approachable she is. I am on the opposite end of the spectrum where I just don't understand how someone could not like her, lol. To each their own.
For males, their pools of heroes are far larger to draw from. I love Data and hate the idea of him being gone as well. Males and females love him alike, but not usually in a hero type sentiment. It doesn't mean he's loved any less, just fans see him in a different light.
I will agree, Data is more popular than Janeway overall, which isn't a big shock being TNG is also the most popular Trek, but of course I think his popularity transcends that fact alone. Data is a character many fans could emotionally connect to and empathize with.
But, I don't believe there needs to be a debate or contest on who should be allowed to return or other popularity contest. Simply put: neither should have died.