I've been using silicone cake pans in my electric oven for a while and they work great and cakes come out easily and washing then is also very convenient. However I see that there're lots of traditional metal cake pans of the same form in shops and so I guess they are in demand.
Why use a metal cake pan and not a silicone one?
Dark metal pans provide superior browning for breads, muffins, and the like that are better with a crust on them. In my personal experience, foods do NOT release well and they are NOT convenient to clean. I actually have thrown out my silicone muffin and loaf "pans" because of their abysmal results. I've never baked a cake in silicone, though.
Wouldn't it have to do with insulation? A heavy, well insulated cake pan results in less doming of the cake. If you're baking a layer cake you want minimal doming which mean less trimming to get everything even. Also, I believe you're supposed to get a more uniform texture since the rise is more even.