There are practical reasons for it. My business website gets 98% mobile traffic. Pretty much anything I'll do about it, I'll do with mobile on mind. If the original design wasn't responsive by default, I don't think I'd even implement a different view for the desktop.
Maybe you get 98% mobile traffic because your site is unusable on desktops?
Was it at least to add features? to improve features? No, there are less features, it takes more operations to achieve the same features, and there is a whole new set of bugs, while the previous set had been corrected along the years.
Moreover, the result is generally more sluggish and ressource-consuming than the previous version.