@Evat Sure, people might have a favourite cake, or two, but surely that's not all they like or ever eat. Are you saying that when they visit a relative's wedding/birthday or some event that has only a single type of big cake, they won't eat it if it's not their specific favourite? Even if you eat cake once ever three months, it doesn't mean you need to pick the exact same thing every time if you can choose. If someone refuses a cake brought as a present because it's not their specific favourite, not because they are allergic, they deserve to lose a friend and be isolated.
There are lots of varieties because people like to try and make different things. If it's commercial, it's called competition and trying to attract customers by offering something new people might like to try, making yourself stand out from all the other bakers. I've made quite a few cakes during my life, and while there's one specific variety I've made a few times, otherwise I've tried a whole lot of different things. All have been very well received.
I don't know where you live, but perhaps the culture is so different between that place and Europe (in general) that we simply think differently.