Precisely.
There aren't many 50-page essays on political philosophy that are read by millions.
The novels, clumsy though they are, worked well enough, much better than the exceedingly reasonable and sane works of Hayek.
A success is a success, even if it is achieved in an inelegant manner.
Now stop for a moment and imagine the potential success if she had been a good writer ;)
More seriously, I think it's fairly obvious that the reason it winds up on Great Books lists is not because it's a great book - far from it - but rather because many people find the politics underlying it to be appealing. Realistically, you can sum up the whole book as follows:
Dear Reader:
Socialism really sucks, and it's even more insidious than you think it is.
Love,
Ayn
Now, as appealing as that message is, does it really belong on a list of great literature? I think it doesn't, because literary merit is as much about execution - the art of writing - as it is about intent.