Because people have a need to glue things to other things
Rubber to PlasticFor strength, we recommend:
But for large areas, and a smoother application we recommend:
A less toxic, and unfortunately, not as strong option is:
There are so many kinds of plastic its hard to give advice here that applies to them all. If possible try a small test in an area that doesn't show.
Some plastics have a smooth surface finish that can be sanded off with a 120 grit sand paper, for better adhering properties.