Why are there so many programming languages?

No one language does everything equally well. Haskell is probably one of the most flexible in that regard, in that you can create domain-specific langages as needed and use just about any programming model. There's even a joke monad that nicely implements C-style state, for loops, etc. You can manipulate raw pointers, if you really want to. But even most ardent Haskell zealots will tell you it's not really the right language to write hardware drivers in. (Same applies to Lisp.)

The we have history. C is 50 years old. There's been some new ideas since, but grafting many of them on to C would make C a whole other language. Like C++. C++ is built around a particular programming model (native code and C interoperability). Are we going to move to a virtual machine platform? Then why not tweak the language to work best with that and the libraries of that environment? And so Java and C#.

Inventing a language is also just a hobby for some. And sometimes they catch on. Same with small languages intended for a bespoke role but which grow beyond it.

There are multiple reasons, such as:

1. Different programming languages are good for different purposes.

2. Some programming languages have what some people (including myself) consider to be problem in the other one.

3. For making an experimental project to see what it is working.

4. Just because you like to invent a programming language, like you can think of to invent other stuff.

(One of the significant problems (although there are many others, too) that I see in many newer designs is Unicode. Also, some consider GOTO harmful therefore omit that feature. No! Unicode is much more harmful. If a programming language has GOTO, you do not need to use it and it does not affect use of libraries, etc. If it has Unicode, this does affect use of libraries.)

Seriously programmers have a big not-invented-here complex. No other scientific discipline has so many needless incompatible varieties of its tools

On the other hand programmers have somewhat smaller egos than some scientists

Programmers like making them.

Because it's relatively cheap to build a new one.

Obligatory xkcd: https://xkcd.com/927/