It is because her ideas are polarizing and untenable. She supports capitalism to an extent that disregards all else. She is more an ideologue than a serious thinker, despite being very rational. I have read three of her major works and I have to say, there are many things she just does not consider. For example:
She believes in the entrepreneurial spirit, to create something out of nothing, wealth out of the wilderness. She believes in the independent spirit. It is a very uplifting viewpoint... until you consider the fact that entrepreneurs don't create something out of nothing, they create something out of something, with the assistance /collaboration of many people along the way, not their own bare hands by themselves... and her characters are mostly resource barons, people who made it big in the steel or coal business, dreaming of lands unspoilt by socialism/government interference. She is unrealistic because she doesn't contemplate the possibility of resource depletion and environmental safety. She believes that people can make great things (of course it is not about the money!) out of their bare hands as long as they have great vision and ambition.
She contradicts herself in many ways. She does not believe in socialism yet one of her heroes designs really great housing for poor people, which would have been his crowning achievement and helped people. The fault was that the manufacturers were greedy and used cheap material for the houses, so that they broke down after a year or so.
Also is her attitude towards women: she obviously despises most women who act in motherly roles or appear to be victims of their circumstances. She cannot understand why they can not rise above it. Her heroine is a woman who excels among a world of men, in one of her stories her heroine marries a man she despises and ruins him with her frigidness, while also making the man she truly loves suffer. The woman does it as a matter of principle, to prove a point (which I still could not logically fathom after re-reading it). The woman also happens to be born a heiress, with stunning beauty, obvious advantages that do not make sense with her standards for the self-made man. So Ayn Rand also espouses rather sexist viewpoints that seemed to sit very well with the men of her time.
It is uplifting, crystalizing experience to read her work.... until you actually think about what she is saying.
