Before smart phones became something for everybody, 99% of "gamers" would game on lottery tickets, casinos, slot machines and such. They are still the majority and they want their slot machines, where they don't have to think or learn to progress. Computer / video game tropes are just an aesthetic to skin a slot machine on your phone.
Some truth to this, many people playing mobile games would never have owned a laptop/PC/console. They play these games on the commute or while watching TV. A "full fledged" game and it's large upfront costs wouldn't interest them.
