If you look at best sellers, they are commonly full of blocks of exposition and contain frequent repetition of facts. Most writing courses and books tell you not to do these things, so why are they there? Because a some readers don’t read carefully.
Now I can’t claim to know why they don’t. Maybe they skim read. Maybe they read while keeping one eye on small children, or an ear on the conversation behind them on the train. Maybe they only ever read at the end of the day when they’re tired. Whatever it is though, you can guarantee they will miss things that are spelt out in your text.
And you’ll inevitably come across this if you get your work critiqued by enough people.
It is possibly the most frustrating feedback to get when someone, with the best intentions in the world, says that you haven’t explained something when you have quite explicitly and often in the sentence right before the one they’ve marked in the text.
After the first time this happened to me in a crit group, I decided the only way to make sure I never did it to someone else (and I do hope I haven’t) is to always read twice. This has other benefits too, but ought to mean you don’t miss things on second read that maybe you had on first read through.