They (or probably just the form) don't like dots and/or too few characters in the field.
As sibling says you can actually enter anything you want in the "CARDHOLDER NAME" field 99% of times. For years I type "$BANK NAME" or "$BANKNAME CARD" (note the space) there and I never been denied.
With the move to teh chip cards and later to PayPass (which doesn't even transmit your card number in any meaningful way) rendered inclusion of anything viable there meaningless.
> There's something about payments that apparently I consider more "holy" than other things.
WEll there is always some idiot what would make it hard for everyone else. Like web designers who do ahve a very... interesting understanding of the outside world (people with Verylonglastnames-SometimesDoubledUp? living on Cultist Monks Revolution of May 1111 year Street? Don't kid me, they don't exist!). Or admins who made you think twice to enter bullshit in the form because the scary red letters says you would need a national ID to receive the package (and names there and in the receipt should be the same!) only for the courier just give the package and be on his merry way not even bothering to check anything (and sometimes forgetting to take money for the package paid in cash, lol).
For now I only know where you need to give your real (ie printed on the card, not your real one, lolagain) name is when the card data is processed manually. The only country where I know it still exists is US of A, last year friend of mine needed to fill out a PDF form (thankfully electronic without the need to print and send it physically!) to pay for Untappd Business.