Games that were created specifically to appease to the people so motor skills inept that they become shallow husks of actual titles, withering in the shadow of legitimate gaming experiences.
Wii Sports, for example, is one of the shallowest, shittiest sports games ever created - a series of sports mini-games stripped of every compelling element involving those respective sports and any modicum of strategy and competitive force and dumbed down so that game haters don't have to think about where their fingers are for more than two miliseconds lest they be offended by having to utilize more than one brain cell at a time. Baseball? Fuck that shit, automated outfielding! Automated running! Automated everything! Fuck, basically it's a homerun derby! Tennis? We'll handle the movement for you, that's far too complex! Only Bowling, by virtue of how fucking simple it is in the first place, remains unscathed from its real life counterpart. Stripped of any and all appeal to true sports fans.
Thus, a "casualtard" genre is any game that has been 'tarded up so that you must utilize the least brain power necessary to become competent at the games shallow, skeleton game design. Most casualtard games are similarly glossed over with a generic, glossy exterior meant to offend nobody and appeal to everybody in the most unassuming, forgettable fashion.
But of course we all want to hear the amazing story about how NINTENDO got yer whole family playing games. It's so amazing it almost brought a tear to my eye. That is totally worth the shittying up of the industry. I got pictures of my nephews and sisters playing Wii Sports on launch day if you want to share them. 'Course, like most families on Earth, my family never touched Wii again outside of that launch week. 'Cause they hate games and weren't going to start liking them now just because they were made even dumber.
Alternatively: We've been over this a hundred times and you've heard the explanation a hundred times. Frankly I'm surprised you still give a fuck that people hate these garbage games.