Does anyone know why she was cut from HomeLand and replaced?

I'm going to guess they wanted a younger or younger-looking actress. Morena Baccarin looks significantly younger than Fraser, so that must have been a consideration.

Understand what you are saying, but once she was chosen all that should have become moot. She had to had gone through a lengthy process to have already been billed as the character. She must have done something to be fired. I feel she has a quiet beauty but she was not well known in America. Baccarin is better known coming off of the failed series V. Heck who knows, Maybe Baccarin was the second choice and they decided she would fit better. She is much taller looking and even if I don't agree she has a more captive face than Laura, she must in some way had a better {fit} with the lead.

It was a blessing in disguise, she went on to star in Breaking Bad, a much better show than Homeland.

It's not always about an actor doing something to be fired, or someone not liking her...etc. It could be, for sure, but that isn't always the reason.

A lot of times you can like the idea of an actor being in a role more than you like them BEING that role. You see or know an actor from something, maybe your favorite movie or a great show and you think "I want to work with them. Oh, they'd be great for this." And you go down that road and one day you look at what you have and realize that maybe it was a forced decision on your part (or other producers/execs) and it isn't really working the way it needs to.

You rewrite pilots so much (all scripts, really) that sometimes when someone gets cast their role is significantly different when you go to camera than when they were brought on. For a series lead like in Homeland that character will be rewritten a ton before it gets to camera.

You never really know. It just takes one producer to get nervous or change their minds for an actor to get fired and replaced. The reasons can be endless and sometimes it's for the benefit of the product and sometimes not. Good actors find ways to be successful anyway.

Laura Fraser is better known for her sex scenes in her roles and in this character it really is not needed. Also she is very short and the two people she would be opposite are very tall.