Kindle books have truly terrible formatting and editing in general. Some are riddled with what look like OCR errors; in others, blockquotes and italicized regions start and end in the wrong places. Images are in awkward places. Sometimes just paging left and then paging right causes the page boundary to move.
The main reason, I've heard, is that even if the Kindle format and reader app are reasonable (and I can't vouch for them), it's on publishers to put their books in the right format. They have no idea how to do this, so they outsource it. Some publishers probably don't care about or dislike the Kindle platform.
I find it really, really sad and bizarre to read books with so many errors. Maybe you haven't come across a really bad one yet, but since it varies by publisher (and I'm talking about big, mainstream publishers), just wait, you will.