first of all for your knowlwde
1. JIO bought spectrum from the auction and under UPA era, not NDA.
2. remember that time when telco used to charge around 6 rupees per minute(I'm sure you must since you're using computer since colonianl era) that time reliance under Mukesh Ambani sold phone at super cheap price and at super cheap call rate i.e free calls from RIM to RIM on 440 plan and that my dear unleashed the true potential of telecom in India.
3. because of JIO whole generation leapfrogged from 2G to 4G and I don't think anyone in the world had given free data/calls/SMS for 6 fucking months.
4. last, don't think cartelization wasn't happening before the advent of jio. since AVI already control 75% of market & whenever airtel used to increase its tarrif, voda and idea follows.