Can anyone explain card linked offers?

I’ve noticed card linked offers on swagbucks (US), Quidco (UK), and cashrewards (AU), where you link your card to a Cashback offer if you spend in general retail. Makes lots of sense to me and seem S like you can earn a good % on your daily spend.

Am I issuing something? Why isn’t everyone doing this???

It seems widespread, but wondering who is pulling these deals together- can I register with one service and get it everywhere?

.....so many questions!