I can speak to why there are alot of implementations of Lisp and Scheme.
Scheme seems fragmented because a lot of research work use it as the primary tool. For example, you have languages like Larceny which were primarily designed to study Garbage collections or even probabilistic language models using Church Scheme.
The ease in which Lisp and Scheme allows you to create new languages and perform exploratory work has spawned a lot of newer implementations.
And People also come up with newer implementations for a specific goal in mind. For example, Bigloo Scheme was created in order to enable Scheme programming style where C(++) is usually required.
Scheme seems fragmented because a lot of research work use it as the primary tool. For example, you have languages like Larceny which were primarily designed to study Garbage collections or even probabilistic language models using Church Scheme.
The ease in which Lisp and Scheme allows you to create new languages and perform exploratory work has spawned a lot of newer implementations.
And People also come up with newer implementations for a specific goal in mind. For example, Bigloo Scheme was created in order to enable Scheme programming style where C(++) is usually required.