There are both planetary and geo-political reasons for this hurry. India, Japan and China all are racing to become the first Asian country to reach Mars.
The first Chinese mission to Mars called Yinghuo-1 failed in 2011 alongside the Russian Phobos-Grunt mission with which it was launched. In 1998, the Japanese mission to Mars ran out of fuel and was lost.
S K Shivakumar, Director of ISRO Satellite Centre, Bangalore says, "Mars gives us an opportunity in terms of its rotation around Sun and all that. We found that there was a good opportunity for us in 2013. Honestly as a technical person we did not look as to whether China is doing it or not."
ISRO's arguments that national pride was not to some degree the driving force behind the haste, however, are not very convincing considering the fact that it opted for a sub-optimal low power launcher, the PSLV, as its preferred vehicle for the first Mangalyaan mission. The more powerful rocket, the Geo-Synchronous Satellite Launch Vehicle, is out of commission, having suffered two back to back failures. This was possibly the reason why this small rocket was chosen for this big national mission. (Full coverage)