Because it is hard to get back the money from them !!!
I bought an electronic item on 14th Aug and it got shipped in 2-days but it did not bet delivered. It was on the way to Yelahanka warehouse which is just 3-4 KM from my house and God knows where it went. I called them twice to expedite the delivery but nothing happened. I am not sure what this Ekart logistics is - whether it is outsourced or is it also part of Flipkart? But do not think that Flipkart will delivery in 2-3 days time, it is not the case, all the time !!.
Losing patience, I cancelled it on 28 Aug and in the cancellation acceptance e-mail, they say that:
"If you have already paid for this order, your refund will be initiated in next 2-3 days and you will get separate notification with further details."
It is 9 days now, and I have not got the refund even after following with them 2 times.
Moral of the story is:
Flipkart does not deliver promptly all the time, and buy using cash-on-delivery (CoD) when that option is there for your product.