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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.
Each languages have its own advantages and disadvantages, and so each one will be better suited for a particular project, but less for another.
It is true for some languages, but a lot of them have mostly the same advantages and disadvantages.
In some case, a language X could have all the advantages of another Y, if the working force were united on it.