@abhishek.balaji - I understand the reason.
I am not sure how many 450s are out there and how many will be interested to buy a TPMS. The volume and the effort to do this may not make financial sense to Ather. In fact, based on the 4G rollout experience, you might want to avoid any retrofitting.
But, 450 is just more than that. It deserves special attention. Until the last 450 runs on road (may be at least for 10 more years), it is going to bring smiles to every one on Ather.
So, not just for TPMS, please keep 450s in your mind and look beyond financial metrics.
Is it an external sensor? I believe so, considering it can be a DIY installation and easy for Ather.