Well it's just that to support another language they need to make solutions for every problem in that language to test that it's actually possible and they don't want to do that.

and on that page it says:

    Each submitted source program must be written in C, C++ or Pascal, it must be smaller than 100 KB, the evaluation server must be able to compile it in less than 10 seconds and at most 256 MB of memory. No other extensions different than the ones listed above will be run.

They put Python and Ruby on the machines so you can write a script to generate testcases, you can't submit programs written in those languages