Hey! I think these backgrounds are quite nice and work very decently. The only thing that bothered me about the cart image, perhaps, is that the bubbles don't really form any shape to lead the eye. I think they could have been used more purposefully to make an interesting shape!
Whilst I don't think your backgrounds are an issue in the two images you've posted, I do think not "afterthinking" would be a good approach. You posting about this has made me realize that for a few years now, I've not really thought about the background as a 'background' anymore. Ever since I started thumbnailing and planning out whole images, I no longer draw elements separately - the background is as significant as the foreground is, and they must ideally work together. A cloud, a branch, a path can all help lead the eye and has its purpose.
Bottom line is that I think both of your examples look great! I'd have a hard time pointing out anything to criticize, and I don't think the focus is off, either. If you were to also use colour, you could easily draw more attention to the most important element with light or colour, too.
But if you yourself think that backgrounds aren't part of your process, I guess I'd recommend doing some thumbnailing exercises where the background as well as the main element are just shapes and tones that need to balance each other out! That way when you fill in those shapes with actual background elements, they can support your overall image structure.