Some of us are slow readers, and just reading the raw amount of words is a limitation, even before we get into how difficult it is to understand.

I've bumped into books (and other writing) where there's simply far too much chewing to get to a bloody point. Every passage has some lengthy aside about irrelevent matters. Often personal bit. The late 1990s / early 2000s highly padded tech texts were the worst for this. Que is an imprint that comes to mind, and many of the "24 hours" type books. O'Reilly and No Starch were usually (though not always) better. The old AT&T Unix classics are the opposite: concise, clear, and highly useful.

Vendor docs are often the wworst -- simply repeating descriptions already apparent from interfaces or systems whilst providing no insight whatsoever to how the tool is used as a system.

The problems this causes are at least threefold:

1. The documentation is ineffective. It doesn't convey useful information.

2. If you're trying to find useful passages, yo've got to chew through far too much crud.

3. The books are huge and heavy. Carrying one means foregoing two or three other (useful) books. And they simply weigh too damned much.

I suspect crowding out other books for shelf space was part of the strategy.

Exactly. Writing well isn't about listing facts. It's an art. That's not to say works can't be overwrought. Buts it's also not to say that long needs to be short.

right, writing's about the useful order of the facts.

Sure, some books are too dense. But honestly, I've only met such in mathematics and theoretical physics.