@irvmullSuch imaginations have to be fueled, encouraged, repeatedly, as it's a leaned, rather than a natural skill. Once upon a time, schools would actively focus on providing everyone with those skills, though now, if the parents aren't up to the task, most never learn it, just like active readers tend to encourage their children to read by setting an example.
Heck, in our family, my father would actively leave books open on a table with a book mark in it. Since I was an active reader, I only noticed it when he set out 'sex-education' books, encouraging us to read them, so he wouldn't have to have those always awkward talks.
Yet, for my sister, she'd active read whatever he was, and thus, when the book marks moved, she'd keep up with them, even when they'd progress at a rate faster than either of them could easily maintain. Thus, it also encouraged her to continually stretch her limits, pushing herself to improve her concentration and focus.
In fact, it worked SO well, she went on to not just graduate with honors, she also got a necessary Masters, yet kept going, earning three separate doctoral degrees, in unrelated fields. So it almost became an addiction for her, always needing to continually push herself to learn more, never settling for a single career.
So, you can do that, leaving books lying where no one could miss them, but in general, reading to children when young, actively encourages them to read. This is evidenced by young mothers taking college or graduate courses, who'd often read their texts aloud. Those kids, not being raised on overly simplified 'children's stories', would then develop the ability to grasp complex concepts and process them, because they were more used to the adult sentences, while those raised on children's books, tended to remain on a remedial level for much, much longer. As then, it took a more significant effort to progress to the more advanced levels, as they'd essentially have to 'relearn' how to read.
Yet, as readers, most of us are more adept as dealing with words, not requiring the visual images, as for us, they're simply not necessary.
However, I took a different approach, where I wouldn't illustrate the story itself, but I'd use specific images to 'capture' a certain 'feel', so images of a rifles, bullets and wooden crosses over impromtu graves for a western, as it would better set the readers' expectations, as if the story changed focus, those isolated images (usually section images, covering a series of related chapters) would only change when the story's focus did.
Again, it was essentially 'prepping' the readers for what to expect, without having to spell it out or reveal what was likely to happen (i.e. spoilers). Yet, not everyone needs such change of focus signals, though many do. So it's largely a toss up. No one actually requires them, yet some benefit from change of focus 'prompts'.
So, if you don't, it's easy enough to simply skip over them. Yet again, I'd rarely do them frequently, only for significant shifts in content. And, my readers generally agreed, as the books with those sorts of images, generally sold better than those without.
Again, they weren't necessary, yet most viewed them as an 'extra benefit', which they couldn't get anywhere else, a case of extra value in my stories over other's novels. Beneficial, not required.
Yet, that's not necessarily a sign of those without ANY imagination, as I've NEVER written simple books, as my text tends to be quite dense. And I'll often NOT spell things out explicitly, forcing the readers to guess what's not detailed, further drawing them into the story.
That's something you don't see often in literature, yet it is common in the best-written stories, as most advanced readers tend to 'read between' the lines, guessing where the story is headed, so by leaving those details out, and 'signaling' the change in content, they were more deeply involved with the story.
And when you see that obvious an increase in sales, you tend to focus on those elements, as otherwise, there'd be NO point in adding them.