Well when Carol's popularity begins to drop they will need to do something. Carol vs Shazam with Shazam possibly moving to the MU for good would be interesting. If nothing else they can make it a huge sales gimmick to artificially boost sales for a bit.
Given that Marvel already has characters that are Superman analog's or "inspirations" they might as well get the biggest one of them all
Also marvel could use a character with a more positive or sunny disposition
Even before Carol, there has never been any incentive for Marvel to make a deal. Back in the "dark days" when Marvel had to struggle to find a way to use the mark every few years, there was zero incentive. They don't need to do something. And there's even less incentive now that she's a billion-dollar star.