We have a number of comments making a distinction between those self-identifying as MO who don’t fully keep Halacha (in various different ways) and attribute their halachic non-compliance as being an “MO shitta” and those who self-identify as MO and do fully observe Halacha. But I think it is fair to say that a lot of those who were MO and fully committed to Halacha have over the years and decades stopped identifying as MO and identified more with and often joined chareidi communities and sent their children to chareidi yeshivos.
At this point I do think that a majority of self-identifying MO are what is called “Left-Wing MO” and what is called “Right-Wing MO” is a minority.
And, really, what reason would someone fully observant of all Halachas have to identify as MO rather than with a chareidi community? You have many chareidim who go to college, work rather than learn (some starting to work before they’re married and others later), etc.