Rabbits are commonly used for research because they're small and also docile, easily restrained, cheap to maintain, and breed prodigiously.
So the rabbits make a good animal for testing products and researching products on.
Another common animal used for research is the guinea pig because they're easy to breed as well and make it easy to do research on.
I personally think it's cruel to do research on rabbits, guinea pigs and other animals but there's not much we can do and we do need the research done on the products before humans use them.