Why isn't Lizzie McGuire talked about in the way Hannah Montana and That's So Raven?

Because Hillary Duff isn’t as famous

It's because they didn't do as much advertising for her back then, and Hillary Duff wasn't infamous, or gay, or connected enough to get anyone's attention like the other two did. Her career in both acting and singing also kinda fizzled out when she got married the first time and had her first kid.