Because she turned 30.

her dad can go suck a nut, sorry but she is a great actor and her breasts and face/hair/eyes are immaculate... if angelina jolie can get work at her weird age and looks then so can Thora, like i dunno maybe put her in a T H O R or marvel comics movie Hollywood!
she could easily play the scarlet witch or some other character in the Thor universe. her beauty demands someone give her some good roles.

So weird, almost 15 years ago she was like the "IT" girl, thought she was goign to be huge. Sad to see how her career ended up, and she was truly a gorgeous star. Seems like her dad really screwed up her career, I've heard some allegations that he is in some weird "relationship" with Thora.... not sure if it's true, but by this point I wouldn't be surprised.

The rumors are pretty weird.

When someone acknowledges they're not always easy to work with, they must be difficult to work with. Producers can forgive aging, if the lady is really pleasant.

jrichardsingleton.blogspot.com

Aging? Uh, since when the hell is 30 old for anybody? Only people under 25 and little kids are silly enough to think 30 is old--geesh.

30 year olds only watch movies with friends or their family/kids, which means certain age groups have different demographics, so if she is 30 18-25 year olds wont think they can relate which limits the movie offers she could receive already, so if her dad is further denying her role offers for whatever creepy or rational reasons it severely limits her role offers.

Yeah............consider herself blacklisted,to a point!!!!

It's mostly her dad, Jack. Symptoms of incest..plus if you've seen Petunia (which he helped produce) too much pot smoking.

One way to debunk rumors is to just think about how idiotic they are. How much control is an incestuous father really going to have over a 30-year-old woman, especially if she's a celebrity? And why would a controlling, incestuous father ever push his daughter to become a celebrity in the first place? And why would Hollywood discriminate against an actress based on nothing but stupid internet rumors? Is Richard Gere washed up today because he was allegedly abusing hamsters (by sticking them up his own ass) back in the 80's? Maybe father and daughter are close and maybe they are "difficult", but that doesn't mean they have an incestuous relationship.

I think this all stems from the(probably true) rumor that her parents were once porn stars in the 1970's. Well, there was a lot of swinging sex going on back then and just because some people did it for a living doesn't necessarily make them any creepier than somebody that attended 70's "key parties", which a lot of people's parents might have done (but probably aren't going to tell you about). I saw old footage of Thora Birch's alleged mom Carol Conners being interviewed on an old 70's cable access show. She acted like some ridiculously oversexed moron, but she's obviously really smart in real life. That was an ACT. Porn stars--in the 70's at least--were actors, like legitimate stars. Nobody thinks that if Clint Eastwood's grandson reaches for the last waffle, he pulls out a .45 and hisses, "Go ahead, make my day!". But people will believe any kind of sexual crap about a former porn actor.

I'm sorry but I don't believe everything I read on the internet, especially when there's no evidence whatsoever and it's not very believable. .