Languages In India

It is pretty surprising that there should be so many different languages in India. Considering that we started off with 2 or 3 seed languages (Sanskrit, proto-Tamil, anything else?) AND the huge amount of contact the different pre-British kingdoms had with each other, people should really be talking almost the same "evolved" languages. There should have been 2-3 languages in the country.

What I mean is ... why should people in state of Gujrat speak a language different than the people in Maharashtra? Both did evolve from the same Sanskrit (prakrit?) root. I do hope there was trade and diplomatic contacts between the two regions which hopefully involved talking. So why did they go in two different ways?

Another thing that bothers me is the absence of Greek, Kushan, Scythian and Parthian influence on any of the so called "North Indian" languages. All these Sanskrit derived languages should have been influenced by the invaders. Compare those cases with the influence of Arabic or Persian on Hindi. The latter seems to be more significant. Is it that there was some influence of the ancient invasions and we have become "used" to those changes in the language?

OK, enough babbling for now ...