Must have something to do with the html pre and div tags that everything is enclosed in.
I found a trick that worked.
Tap-hold at the very top, just before the text begins, but below the header bar. Sometimes I get a complete select of everything. Sometimes I only get the blank line just above the first line of the text.
If you only get the first line, then drag the right handle to the right, and everything is selected. It doesn't work if you drag the bottom handle.
Anyway, doing this I managed to copy the entire text using Safari and then paste it into Notes.
Weird though.