There are many for the same reason that engineers don't make a single tool that does everything. There are so many different contexts for programming languages. At the core they allow expression of a solution. This draws on the context the language provides. More context, more concise solutions, but less generality. Also might incur performance penalty, which is a drawback in other circumstances. It's also hard to get a good balance of things in a language, and as things evolve they get used in different ways than when they were designed. And people start using a language and don't want it to change too much after that, so that language is kept around and new ones serve other uses.