That's not really a fair criticism of the movie. They were in the middle of an invasion on Star's castle, it was about saving each other's life not talking about their feelings. There wasn't any time.
They also did address the awkwardness. Or rather, they addressed where they each are. Clearly Star has no qualms about letting Marco know how she feels, she literally stole his sweat jacket to smell it and took the first chance she got to hug him. She also called him cute to his face when he put on the beret. Now look at Marco, he pulls his hands away when Star goes to hug him and waits several seconds for her to stop before realizing that she isn't going to. He even moves his hands further backward when they zoom in. He's clearly hesitant to embrace his feelings for her, but he still has them.
The rest of season 3 is going to be focused on them ironing out the awkwardness in their relationship. But the movie was go time. They had to defeat Toffee so it wasn't important to bring up "us" or Jackie. The staff said season 3 had a lot of crying scenes, so the suffering has likely only just begun.