The first time I had a cancelled flight, I had no idea what to do.
I just rang my travel insurance company up assuming they would sort things out for me then and there but I had to sort things out myself and then claim later.
I'm sure most people would assume the airline would deal with things if something goes wrong rather than being expected to do everything yourself.
Not everyone has £10k+ limits like a lot of people have here.
Maybe funds and already allocated to something or are due to be i.e. car hire, hotels taking £150 a night as a security deposit that doesn't get returned for 1-3 weeks etc.
A lot of people may be happier with cash so may be carrying that (or in the bank) rather than on a card.
It does give the impression here from various posters that the airline is actually doing you a favour by possibly letting you fly. If something goes wrong, it's always your fault and you should be prepared for the consequences.