I wonder how much curly quote usage influences things. I type things like curly quotes with my Compose key, and so do most of my top similars; and four or five words with straight quotes show up among the bottom ten in our analyses. (Also etc, because I like to write &c.)
I’m not going to try comparing it with normalising apostrophes, but I’d be interested how much of a difference it made. It could easily be just that the sorts of people who choose to write in curly quotes are more likely to choose words carefully and thus end up more similar.
Curly vs. straight quotes is mainly a mobile vs. desktop thing AFAIK. Not sure what Mac does by default, but Windows and Linux users almost exclusively use plain straight quotes everywhere.
My impression is that iOS is the only major platform to even support automatically curlify quotation marks. Maybe some Android keyboards are more sensible about it, but none that I’ve used make it anything but manual.