I get that the answer here is necessary for plot/character development reasons, but it still makes me kind of sad that the answer wasn’t “art.”
It’d be consistent with depression, though… especially if he’d already tried and found that there just wasn’t joy in it for him any more.
Don’t forget that at this point, Sam probably doesn’t even know that Steve used to art. Sam knows Steve more as Captain America than as Steve (though that would be the case with most who don’t know steve personally). So Sam’s response is the most logical. I have absolutely no doubt that if Sam knew about the art, he would have suggested it.