Not sure about OP, but for me it's about convenience. My pet peeve is credit card forms. Do you know what % of websites I've used that have at least minorly broken credit card forms? It's literally 99%.
Random common issues that are annoying but can be fixed:
- autocomplete doesn't work at all
- autocomplete only fills in half the fields
- autocomplete only fills in 1 field at a time
- autocomplete doesn't interact correctly with the rich widgets they provided for date picking or zip code
- autocomplete doesn't play well with js validation, which is only on callbacks for typing. Now I have to go backspace and re-insert the last character of every field so it doesn't think it's blank
- my town name has a ' in it. complete fucking crapshoot on whether sites DEMAND or HATE the '.
Common issues that are complete fucking messes that can't be fixed:
- javascript between fields fights over edits between them and I can't get the form simultaneously filled out correctly
- rendering issues on mobile leaving fields not visible
- autocomplete doesn't work and I've for some reason forgotten my CVV again and don't want to go get my wallet
I could go on and on. It's amazing how hard it is to get this right and how obviously nobody tests the flow where PEOPLE GIVE THEM MONEY which as I understand it is the primary purpose of these places.