Er, The Guardians of the Galaxy is very much James Gunn’s baby. He’s not going to let it be compromised by executive meddling.
This, like the footage used in the Rogue One trailers is all the marketing department’s idea. They know that audiences loved Groot and so they’re emphasizing his character.
They also think the general audience is stupid, so of course they slapped baby Groot on there. “This poster doesnt have any pictures of the characters. How else are those dolts going to know what movie this is for?!?”
All that to say, you’re making a mountain out of a mole hill. 😛
oh and here’s The Extended Superbowl Trailer for anyone that missed it!