Why over the course of time have more programming language been developed?

Different types of programming languages exist because they each Excels in a different aspect of programming, and in fact many languages are invented specifically to fulfill a niche that existing languages or language families don't handle as well as programmers would like. The two main distinctions used when determining what languages are best for a given task are low-level vs. high-level and interpreted vs. compiled.

"Low-level" languages such as C and the various assembly languages grant a programmer the maximum amount of control over memory usage and allocation, making those languages good for embedded devices and tasks where memory is at a premium, while "high-level" languages provide a great deal of abstraction, allowing programmers to perform more complex tasks with less code and implementing concepts such as variable-length arrays, garbage collection, first-class functions, etc.

"Interpreted" languages such as Perl or Ruby are executed by an interpreter program in real time, allowing these languages to benefit from features such as on-the-fly code modification (reflection) and dynamic typing and allowing them to be run on any system with an appropriate interpreter installed, while "compiled" languages are translated to machine code or bytecode, making these languages much faster and more efficient when run (as compilers can optimize programs ahead of time for speed and memory usage).