NCPI (National Payment Corporation of India) – the developer of UPI (Unified Payments Interface) – is apparently the one calling the shots.
NCPI – Roles & Responsibilities
"TPAP is responsible to comply with all the requirements prescribed by PSP Bank and NPCI in relation to TPAP’s participation in UPI"
If I'm not mistaken, TPAP stands for Third Party App Provider. NCPI and the Banks say "Jump!", and the UPI app providers say "How high?" Then UPI app providers say "Jump!", and you say "How high?" If you refuse to jump (e.g., you insist on using an iPhone that is too old to update to iOS 17), the result is that you don't get to use UPI.
If you don't like it, complain to NCPI and the Banks.