I strongly feel that lackluster demand for 3G seems to have made the company cautious about over-investing in LTE (read a multi-city launch) which can be seen by the planned launch across only three more cities (for now). It plans to launch the service across Bangalore (Karnataka), Pune (Maharashtra) and Mohali (Punjab) making it one city in each of the circles won.

What is Airtel's Pricing Strategy for 4G ?
4G LTE Wireless Broadband averages speed of 10-15Mbps [pragmatically speaking] compares favorably vis-a-vis 3G speed of 1-2Mbps. The dongle/modem price at Rs7999/7750 too is relatively high (Rs2050/2450 for 3.6/7.2Mbps 3G dongles) and could come down as scale increases which is not in the short term.

3G vs 4G Plans in Kolkata

Now in the above chart it is clear that Price / MB is lower as your usage increases. Thus they have priced it in such a way that when a user had enough of 3G, he can move on to 4G :-)