Everyone understands the paradigm of double clicking an icon to launch the program or an installer. Many aren't going to understand the exact command they need to type into a terminal to get it to do what they want. This is almost always the answer for why people don't want to resort to using a terminal, discoverability. You can look it up, of course, but there's no good reason imo to not include GDebi for users unfamiliar with that workflow. Other distributions have it by default, but Cannonical is favoring their own tech here over the needs of the users. One more useless roadblock.

My dad runs Ubuntu at home. He's completely computer-illiterate. When I need to help him install something over the phone, it's really nice to be able to have him download a .deb, double-click on it, and it just works. I've done this numerous times over the phone with him... it would take me an hour just to get him to type apt install properly.

For me the struggle is: is the package called libcairo-devel, libcairo2-dev, cairo-dev or something else, i hate running a search everytime