Can be... but won't necessarily be.
There will be people out there who have no clue what it is like to be on a min. wage, low income, running out of money actually meaning the bank account reads zero.
Those people may say 'Oh, I've no money left this month' but what they mean is they've spent what they generally ear-mark for outgoings, they still have hundreds or more in a current account, they still have thousands in savings.
And so they do not understand that when they fail to repay someone the £5 or £10 or £30 within minutes, they are causing that person actual distress and financial problems.
I've been there, I have had people agree to pay on the day, agree to my T's and C's and then come payment time, attempt to pay by cheque (nope, we don't do cheques, thats in the info you were sent when you booked..) and then offer a bank transfer... and then take days or in some cases, weeks, to do that.
So yeah in a carers shoes, absolutely no WAY would I be spending my own money in the hopes I'll get it back promptly, or at all.
OP - I think a pre-paid card is the way forward but I would have a word with the care company and ask if this is normal policy, as asking for a service users card and PIN is really dodgy territory.