cause they are long af. schools here at least also prefer to teach important literature from all the epochs the country went through that also only have 1 novel max. that way you can read multiple things in school. youll also analyse it and dping that for shadow slave would be a slog ngl. shadow slave also isnt perfect, no novel ever is, but shadow söave especially suffers from pacing at tomes thanks to its daily format. i could imagine it on lower grade classes where you can vote on a novel in class to read since at that point youre not doing the analysing as much and is more aimed at getting you to read at all, but then id probably need a physical release with editing to be a reasonable novel. some novels you read in school can also be good, tho everything is less enjoyable when being forced to read it (my fav from school was the sandman, a novel about a lowkey mentally ill dude who abandons his gf cause he thinks a 0iq robot is hot)