I've always thought that Boba was popular for two reasons: the first was the fact that the action figure was released as a teaser for Empire Strikes Back. Hey, I sent away for him! So did every other kid. And with no background to serve as reference, most kids developed their own gripping backstory for Boba. He was a major villain in action figure games ... far more important than he ever was in the films.
And then after the mail-away offer expired, Boba Fett hit the shelves in full-force months before Empire debuted. He was one of the most available action figures at that time ... easier to find than the major characters.
In fact, I remember feeling disappointed to see that Boba Fett and Bossk (another pre-Empire mail-away figure) were so inconsequential to the plot of Empire Strikes Back.
Anyhow, that same generation which concocted grand stories about Boba Fett without any source material is the one that perpetuated and handed-down the tradition of glorifying Boba Fett.
The second reason is the Holiday Special. I was only seven when that aired, yet I recognized how embarrassingly awful it was. I remember going to school after it aired, and all the kids hated it EXCEPT for the Nelvana/Boba Fett cartoon. The cartoon was the only thing that made the special worthwhile, and the Boba Fett character stuck in everyone's mind as a result of the awfulness of the rest of the show.
Boba Fett looks fairly cool as far as design goes, but I never thought he was the best-designed character. In fact I thought the AT-AT trooper uniforms looked cooler, as did the tie-fighter pilots.
I didn't dig Darth Maul a whole lot, either. He's not a bad looking demon-guy, but he's way too cheesed-up for my tastes so I cannot begin to fathom why that character inspired any loyalty.
On the other hand, I totally fell for Asajj Ventress as a result of the Clone Wars cartoon. Maybe it's because I'm a gal. I actually flipped through some expanded universe crap for the first time since the 90's just to get a little more backstory on her ... and I was a bit disappointed, but I still like the character and the cartoon design. I would have taken her over Darth Maul, General Grievous, and Count Dooku ... and Boba Fett.
My husband bought me the Asajj figure for my birthday this weekend, and I found myself making up stupid backstories for her like we did for Boba Fett when I was a kid. I imagined her hunting Jedi at Darth Vader's side after Revenge of the Sith ... still dreaming of becoming a Sith Lord. The two form a tenuous friendship as a result of their youth and their hatred for jedi. I pictured her gradually falling in love with Anakin/Vader ... in awe of his powers over the force and oblivious to his physical deformities. When she finally expressed her feelings for him, he made some comment about how Padme was the only person he'd ever loved, and he could never care about Asajj. Further, he believed that there was nothing left to love in him. Hurt and angry, Asajj attacks Vader and fights with him so violently that he's forced to kill her ... which is what she wanted in the face of rejection. At first Vader thinks that she was one more person who said she loved Anakin only to betray him ... but then the reality set in that she was one more person who cared about him which he killed/hurt. It propels him further into the lovelessness of the dark side.
Then I blinked and realized Lucas would NEVER be able to tell a story about Asajj that could match what I can imagine. If he did tell a story about Asajj, it would be something dreadful like what he did to Boba Fett in Clones. Or worse ... Lucas would have her step in Bantha shit while fighting some wheezing android.