I'm disappointed to see that MS Word has become the default for publishers. Back in 1999 I authored a web programming book for O'Reilly. At the time, their technical folks would begrudgingly accept Word files, but they strongly preferred FrameMaker.[1] Some of that probably had to do with the propensity for large Word files to become corrupted, but it's also because FrameMaker helped authors generate documents with m…
How long has it been since you used Word? The styles are now right on the Home tab in the Ribbon. On my monitor, it takes up over half the width of the Ribbon. You don't have to "pop open" anything to use styles, but you do need to open the styles palette to define and change styles.
A publisher could supply a Word template to its authors, and forbid the author to make any other formatting changes. They could also enforce this by opening the styles inspector and checking for any unauthorized formatting.
An author could also apply a different stylesheet to reformat a text to match a different publisher's stylesheet.
Word is a styles-based word processor, internally. If you boldface some text, Word will create a new anonymous style that's simply the existing style, plus boldface. You could even use the styles inspector to change all instances of that anonymous style back to the original style, or to turn it into a named style.
You can use Word like Framemaker (sans frames) if you want. It's just that most people don't.