They almost have to if they want people to know about it. People are going to see Guardians whether they follow all of the MCU or not. They are that kind of group that attract non Marvel fans.
Captain Marvel was released between Avengers to give some hype. This sequel has nothing behind it that can tie to it. We haven't seen Photon since Wandavision 3 years ago, I assume Khan is in it I didn't finish Ms.Marvel not sure if that was a major hit, Danvers was okay in first movie and has had limited time in appearances after. Great fight with Thanos but personality wise nothing memorable.
This is the GOTG last hurrah so I am not expecting them to sell other projects too much in this during the movie so a teaser or trailer of Marvels is all they can do.