(IIRC the automatic backup was readable, and I recovered most of the work from there. But one of the equations was cursed, and I had to delete and rewrite it. (I probably had a handmade backup, just in case, but it was a few hours old.))
It is typically because they have the wrong mental model of how image placement should work. Floats are floating for a reason.
You should guess again.
With LaTeX the biggest problem with images is seeig them reflow in a place you wasn't expecting because you did not paid attention to what you actually did.
With Word, you even have to fight it to not put images and their image captions on separate pages.
More importantly, with LaTeX the worst you get with images is them looking nice and neat in some other part of the text, maybe at the end of a section or with a single paragraph between them. With Word it's on par for the course to get your whole doc screwed up just because the image reflowed to the next page.
You keep saying this, and this has simply not been true since Word 2007. You keep captions on the same page as their respective pictures using the same method you keep all lines of a paragraph on the same page: Keep with Next in Paragraph options. If a caption (or picture) still flows onto the next page, that is because it simply won't fit into the page without resizing the picture or changing the page margins.
This is only really relevant if you're generating Word documents programatically from other data sources (it's very easy to do this with the MS-provided tools which can auto-generate code-behind for programs that need to make documents like this), but it's entirely possible to end up with invalid OOXML that means the document doesn't load.
Some are recoverable, some aren't.
JS 1 - Haskell 0