[nightpool]

Presumably because the DOM order of the elements is not the actual order of the lines (you can see this with e.g. the blockquotes), so it would be confusing if the user tried to copy the text and saw that all the lines were jumbled up

[rezonant]

It's only the blockquotes that are out of order. If this were a valid reason to disable user selection, then no website with a sidebar would have it enabled. Besides, you could just disable user selection on the blockquotes if that were the reason (not that I'd ever recommend that)

[nightpool]

That wasn't my experience, when I resized the window and new text showed up, it was completely out of order