I think it's because Namco had a patent on games in loading screens from 1995 to 2015: http://kotaku.com/the-patent-on-loading-screen-mini-games-is...

Ghostbusters game on c64 had it when I bought it used in 1991 or 92 I think.

It's a common example for a patent that had a lot of prior art but was granted anyway.

I don't know enough about patents to say if there was a reason the prior art didn't apply, but I know that Namco was fairly protective of it and it was somewhat limiting for people working in the game industry.

Although, loading screens are less common now than they were back then, and I think that would still be case even if such a thing were never patented.

Having minigames during loading or installation was actually patented by Namco for Ridge Racer, I believe. I'm not quite sure about the details since I seem to recall things like invade-a-load on my Commodore 64 at least a decade earlier, but there you go.

Expired in 2015 :)

When I was younger, it seemed so obvious to add a minigame to a long loading screen, I had assumed that there were technical reasons for not doing it.

Not quite the same thing, but DVDFlick lets you play Tetris while your DVD is being authored and burned, which was a nice suprise.