I could watch TV passively (I don't watch TV, but I could). However if you switched my TV for one that received only Spanish - I have enough Spanish that I could understand, but it wouldn't be passive for me, it would be hard work to understand.
How did people get worse at reading, other than choosing to spend time on the alternative activities that I listed? You may be reversing cause and effect.
Obviously I meant mentally passive, not physically passive.
Neither did I.
Anyway, I don't buy the "energy" story, that doomscrolling is somehow low-energy, or even that people can't muster the energy for any activity other than doomscrolling.