This has been a thing for centuries at this point, though it seems to be falling out of fashion. You can find it in style guides already just after the turn of the 20th century and the practice certainly dates back further. Some publications online have stopped doing title case in favor of sentence case, but I’m not sure in physical media. Title Case sets the title apart, may be clearer or catchier at a distance (good for newstands and newsies, I guess?) and I find it easier to read in some cases. Some argue it stems from German which capitalizes all nouns, but I doubt that since this is done everywhere in German and not just in titles.