Noticed this started a few years back, getting worse and really annoys me. Go to a shop - any clothes, supermarket etc. The customer in front of me realises needed to pay. Goes on the banking app and transfers money from one account to the card paying on.
Why do they have to wait til they are being served? Plus many shops, internet signal is poor. Then the staff member has to get a supervisor to save transaction whilst customer goes outside to get a better signal.
Phones have calculators. Add things as you do shopping. Check bank balance. If requires more money, do the transfer. Then go to the tills.