Deterrent is the word here.Off-road mobility is not required for our missiles. Plus India's road network is pretty good and getting better. It's also going to be difficult to spot from space if our TELs looks like regular trucks.
As for MIRVs, its relevation to the public and its existence are not synonymous. Moreover, its relevation doesn't suit our current diplomatic and security needs even if they have been deployed. The US is going to face difficulties back home if it's revealed that India has operationalised MIRV. Plus, this relevation will benefit Pakistan more than it does India. You can say that if MIRV has been deployed, it makes more sense for India to keep quiet about.
All nuclear weapons are flaunted for deterrence purposes.
No point in having a nuclear weapon if enemy doesn't know about it.