It split the community between a lot of different languages, decreasing the resources (documentation, tutorials, class, etc…) for each one of them.

The people improving the programming languages are dividing their work between languages which are mostly equivalent, reducing the rate of progress.

We can only work on a small set of projects if don’t know a lot of programming languages, because of the great diversity of used languages.
So we have to choose between spending a lot of time learning new languages, or restricting the number of projects we can work on.

We have to duplicate most of the tools which help to program in a particular language (debuggers, syntax analyzer, libraries, framework, etc…).
Increasing the work to be done, and decreasing the quality of these tools.