Sorry for some fancy vocabulary words, but when something gets commercialized - when something starts being thought of principally for its financial gain or becomes profit-oriented, and then it becomes ubiquitous - it's found everywhere, becomes inescapable - you can bet that thing will soon become trivialized: we will start to think it is less important, significant, or complex than it really is.
That poster is a great example of this dynamic.
Originally printed with the intention of keeping the British population encouraged during what they knew would be relentless German "blitzkrieg" bombings of civilians, the poster went from 75 years of obscurity to a coffee cup and t-shirt mini-industry in only a couple years. In the past 15 years, it became a meme. And sure enough, it soon became satire, and trivialized.