According to the Cornell University College of Veterinary Medicine, cats typically urinate on the bed for a few reasons, such as underlying medical issues, an aversion to the litter box or simply a preference for urinating on the bed. Cats do not typically urinate outside of the litter box as an act of revenge.
Medical issues such as a urinary tract inflammation can cause painful urination in cats. When a cat experiences pain while using the litter box, it often ends up associating pain with the litter box, which deters it from using it. The cat may use the bed as an alternate urinating site if it becomes afraid of using the litter box.
Cats often resort to urinating places such as the bed when the litter box is too dirty. Unclean litter boxes typically smell of ammonia, which can be offensive to cats. Litter boxes that have been cleaned with strong chemicals can also be offensive to cats. Litter boxes that are too small or that have high sides can make it difficult for certain cats to properly use them, which forces cats to find an alternate bathroom site.
Placing litter boxes in loud areas or in high traffic areas may also encourage cats to urinate in quieter areas such as the bedroom. Owners may have to move the litter box several times before a cat is comfortable enough to use the box.