I only switched to GRUB because of installed defaults and my laziness. LILO was, imo, always simpler, cleaner, made more sense.
GRUB works, but it feels like it's been engineered to be way more than it needs to be, and, in the process, it starts to suck. As an example, I started looking into GRUB theming (hey, a pretty boot screen would be nice). Turns out I could never convince GRUB to use a TTF font and display the table (and items in the table) correctly. That's a feature that may as well not be in there -- if it doesn't work, turf it. I didn't *need* it, but I spent a bit of time trying to get it to work and failing, which I wouldn't have bothered with if it just weren't there. Or there's the interactive boot -- works if you already know by rote all of the GRUB internals, at the currently installed level; completely useless otherwise. That being said, it does still work, and I still use it to select an OS -- I just miss LILO.
Also, LILO was quite explicit about the "you need to run me to update the MBR" ruling. Which I found kind of comforting: if you didn't make the active choice to update your MBR, you didn't make the active choice to break it with a bad config.
Also, diversity leads to better overall design across the spectrum. Any time a competitor is lost, it's sad for the ecosystem as a whole.