Do everyone end up to work as a marketers?

In France, this would be unthinkable. The studies you do are so specialised that you can only end up working in the field that you've been preparing. However, in the UK, you can do any degree and you're very likely to be able to end up as a marketer. Their degrees are specialised yes, but they also prone "transferable skills" that will help you in anything you do. I think it's best to have a bit of specialisation, but not too much. For example, if you've studied art, it's nice to be able to do a job that's only midly related to art. You could end up a marketer for a photo shoot or anything of the like.