Never understood why Paytm's iOS app has to be 390MB. Uninstalled it long time ago.

For most people, its usefulness (cashless payments) outweighs all other inconveniences (terrible UI, too many notifications, download size etc).

Yes, but other apps (Google Pay, PhonePe), with ubiquitous QR codes offer the same at a much smaller size.

I can assure you, 99.9999% of the users don't care about download sizes.