What are credit card offers?

How come a company like Chase didn't have credit card "offers" atau anything like that not too long yang lalu for me.. and now they say I am "eligible" for the Slate and Freedom (this is the card I want within the new year). Citi has done the same thing to me in the past and now I am "eligible" for one of their cards. Yes I know offers don't mean anything and just cause I get them doesn't mean I'd get approved. I'm just asking how did any of this change? When companies like Bank of America, Discover and American Express say they don't have any offers for me.