Why is the intent flow different on an iOS device?

UPI intent is very popular with Android users because it enables them to make payments from any UPI PSP app installed on their mobile phone. The customer selects the desired app on the merchant checkout, an intent flow is triggered, and the payment  is completed by entering the mPIN on the UPI app. The customer gets redirected back to the merchant’s app upon successful completion. 

Whereas an iOS user moves around to the selected UPI app manually and completes the payment by entering the mPIN on the desired UPI app.