Credits are nice sure, but they aren’t required. I don’t think it’s accurate to say that developers are pretending they were the ones who created it by not including attribution. My assets were used in the Mass Effect ride in California. Would it have been cool to get some credit for it? Sure. But they aren’t obligated to, because they purchased my assets and there was no requirement in the license to do so.
Keep in mind though, this is just when it comes to marketplace content. If you want to sell your assets elsewhere and include a usage clause that demands credit placement you’re free to do so. Just make sure people know what terms they are getting before they purchase your product, because as Ambershee noted springing it on them after the purchase isn’t going to necessarily hold.