I imagine the issue is maintaining consensus between the different phone companies. Without blockchain you'd have to have a canonical database run by a single entity, whereas you can use blockchain as the consensus mechanism among competing companies.
I mean sure you could have the government manage the central database but maybe the Indian government is not equip to run such a database. Plus you can avoid some of the problems with high costs or stagnation that can happen with centrally run systems. I don't think there's any particular reason to reject blockchain if it works in this case.
