Why doesn't epoxy stick to silicone? Is there a type of epoxy that does?
There are two reasons why.
First, for any glue to stick to something, that something needs to be wettable by the glue. A cured silicone surface is bristling with uncrosslinked silicone units which have extremely low surface energy and hence are very difficult if not impossible to wet by glues like epoxy. This means the cured epoxy exhibits no adhesion to the silicone surface.
Second, the elasticity of silicone and cured epoxy are wildly different, which means if the joint between them is stressed, the silicone stretches and the epoxy does not- and so the silicone "unzips" from the epoxy glue line and the joint falls apart.
Silicone is not a single substance, it is a very very wide range of different types of materials with widely varying properties! All materials that have several siloxane monomers in them can reasonably be called silicones. This can take almost any shape; foams, glues, coatings, rubbers, oils, powders, gels. 3D printed solids, even.
Some silicones will adhere effortlessly to epoxies. Some even have epoxides in their molecular structure. And some are made to be a copolymer, designed to be coexistant with an epoxy in the final formulation. Some are made to be cured together with epoxy. Others to be cured onto epoxy.
Other silicones will absolutely not adhere to epoxy, silicones are usually quite hydrophobic and can be substituted to be even worse.
I'd say it is more about the silicone, than the epoxy, whether they will have mutual wetting and adherence.