PDFs look and are made to feel like actual books. I see that as the primary reason for people being comfortable with PDFs. Even if their readers are buggy.

Consider the alternatives.

HTML, too much re-rendering and re-formatting.

Word - Oh No. Not in a million lives. Have you seen the atrocity that is the "reading mode" in Word?

Epub / Mobi / Etc - I have never come across good readers.

For what its worth, PDFs are great for reading on larger screens like iPads. I read them on my mobile too, but that's not good for long reads.