why dont som people like tara?

I liked her just fine myself, so I can't say for sure, but I imagine some people probably find her boring. She's really sweet and everything, but she doesn't have a whole lot of personality compared to the other characters on the show. Maybe they feel she wasn't important to the overall story and was just a distraction from the good stuff?

It's also very possible that people dislike her simply because they shipped Willow with someone else. Shippers can be passionate like that :D

I like Tara I just don't like her with Willow. I mean I guess they were cute as couple, but I'm not really a fan of same sex couples. Sorry to those who really like this couple.

I didn't like her as a character because she was uninteresting. Had no charm like any other character, and the relationship didn't feel like it had as much spark as the others. They way they act around each other just isn't interesting. It's like they just decided "Okay, let's put some lesbians together and let the les-factor drive the chemistry". Pretty much just a couple whose defining factor is "Look, they're together and they're witches". They wouldn't be considered a decent couple if it were Willow and a random dude, because there needs to be an interesting character on both sides. Tara just isn't that.

I think some fans dislike her just because they were really strong fans of Willow/Oz. They dislike Tara for "replacing" Oz. Or they dislike the idea of Willow being gay, so they dislike her female lover.

I've also seen some people complain that Tara was boring because her personality was quiet and a bit timid and shy. Personally that was something I liked about her, though.