I think the difference is that Deadpool and Deadpool 2 uses things within the world of the movie for us to care about (Vanessa and Rusty), Deadpool and Wolverine basically only exists on a meta level. Like, wouldn't it be cool to see Blade, Electra, and the Human Torch again? And to let Channing Tatum finally get to play Gambit? But these are not people Wade has any reason to care about, which makes the thing fall a bit flat.Still has some heart, but same as the first two is very much a parody of the genre.
In 1 and 2, the 4th wall-breaking is a sometimes thing, with Wade offering commentary on the movie ("Isn't it strange how every time I come here it's just you two? It's almost like we don't have the budget for more X-Men."), but still having things unfold within the movie's own logic. In DP&W, there's no 4th wall to break, because the whole movie is commentary on the various Fox movies.