That’s solely because it is being updated where as apt-get has not been modified in that way for years. That also only means things like adding extra features like 16.04 gained autoremove where as previously it didn’t have that. The syntax of install and update wouldn’t be changing and therefore not using it because of that wouldn’t really make sense.
There is a lot more to it other than “coloured output” for example apt install handles local deb files better than apt-get.