just a member: Actually, Chassidus was the response to many Jews discontinuance of practicing Judaism.
Modern Orthodoxy was not a new movement. It just had a name given to it after years of being around. Were/are there people who didn’t/don’t follow halacha? Yes, just as there are among the chareidim, chassidim, sefardim, and every other group. There will always be people who don’t feel like doing what is right. Still, the basic beliefs of Modern Orthodoxy are closest to how Judaism was practiced for centuries.