johannes credit cards usually don't have a x2x but an x0x service code, and even some debit cards have that.
Most brick&mortar banks have some kind of overdraft etc. on their accounts anyways so some kind of credit line anyways.
"Historically" only prepaid cards had used that "always contact the issuer online" service code - more general all banks/cards/etc. that wouldn't allow for a negative account statement (e-money... etc.), so it kinda fits bunq's general statement that they don't want to provide credit or make people get into debt etc. With the possibilities of the chip on the cards, you can limit the possibility of offline payments to a certain amount, with the magstripe you only can tell the terminal "yes or no", so you could get yourself into serious debt.
AFAIR bunq rather tries to get rid of old things and only half-heartedly supports magstripe payments in general - wasn't it that maestro magstripe payment are not supported with the bunq card at all? I admit, that I haven't tried yet but I remember something about that (too lazy to look it up now).
And for mastercard magstripe payments you have to enable USA in the geolocking thingy? Something like that.
Personally, I think it's the right strategy, but life is not as easy as with a "real credit card from a real bank".