Interesting! For AWS, DO, Linode etc, I use a debit card with no problem.
Edit: just remembered we're using Google's Cloud Vision API and that's billed to the same debit card. So, for UK accounts at least, they take debit cards.
Maybe it's a regional thing? Most banks here (Ireland) issue debit cards by default and most people don't go out of their way to get a credit card, so they'd be cutting off a large chunk of their customer base by banning debit cards.
Are your debit cards really just debit cards (i.e. bank-specific "ATM" or "client" cards), or do they work using credit-card payments infrastructure? If you plugged your Irish bank debit card number into e.g. Stripe as a credit card number, would it take it?
Edit: just remembered we're using Google's Cloud Vision API and that's billed to the same debit card. So, for UK accounts at least, they take debit cards.