Mass adoption probably won't happen in a way we're expecting it to happen in. I don't think that it will a regular thing to pay for your coffee or dinner using BTC. It may become a way of paying for something online, but I do see it more as a backbone technology and asset of some sort (yet to be determined).
why not? having a kind of a credit card with bitcoins in there ,paying with or without any transactions
Because if you're using a credit card, you're not using Bitcoin per se. You can use a credit card that is backed by Bitcoin (like the Bit-X credit card), but you're not using the Bitcoin protocol that way, since with Bitcoin you can only 'push' money, but never 'pull' money. Credit cards work the other way around!