A game on the other hand can create a sort of rewards treadmill where no one ever really 'finishes'. A book can't adjust rewards in real time to fuel addictive behavior.
Books don't really exploit gambling mechanics, which is what can drive some of the most pernicious addictions.
It's literally virtual building blocks (+ hack and slash combat and crafting and exploration etc). Would you have the same level of derision for kids who sink thousands of hours into playing with lego? Kids have a lot of spare time to kill.
From the way some people talk about video games on here sometimes I assume they think the android/ios market is representative of all of gaming (even then there's plenty of good "buy once" mobile games without microtransactions, the discoverability on the stores is just godawful - presumably to steer people towards more profitable crap rather than what's actually good).