First, some cats do like water. But it seems true (from personal observation and most people's opinion) that most cats don't.
The question has already been asked many times online. Just Google your question!
I doubt one will find peer-reviewed papers on the question but below is a summary of what seem to be the most often mentioned possible reasons I could find. Of course, these bullet points are very hypothetical and I don't know of any research presenting evidence for or against these hypotheses.
Their fur is not really adapted for the water and will very quickly become waterlogged and heavy making it uncomfortable.
Cats are generally speaking quite skittish
Cats may not like the odour of chemicals we put in the water.
Cats love to groom themselves. It is an aweful lot of work to do the grooming after a bath.
Note also that domestic cats are descendent from cats living in very arid areas. The most closely related species with cats are the African Wildcat living in Northern Africa, the Near East and around the periphery of the Arabian Peninsula.
Source
My non-peer reviewed sources are