I get what you say, but for me it's all about familiarity.
if I were writing my own books then having a standard style sheet would make sense, but all I do is tweak to suit my own reading preferences for novels:
which other folks are welcome to hate
fully justified, no hyphens, no widows or orphans, no dropcaps, and no acres of wasted space around chapter headings. Calibre conversion does a lot of that via the extra CSS inputs and filters, then a couple of regexes take out fixed line heights and <a tags, a quick zap of fonts I don't like, set the text indent to 1.5em and I'm about done.
probably take less than a minute to prep new book for reading with that. I also zap dedications to people I don't know & will never meet, epigrams intended to show how much better read that author is than I am, and trailers for other books in the series layout.
i finish off with a quick modify-epub plugin run to fix up the TOC and a page count plug-in run for the pages that I am actually going to read. Once I have read it, I can delete the original format backup also.
I hate reading bought-from-amazon books in their original format and via the kindle app because I cannot suppress hyphens and I cannot customise page turn tap zones.