Accidentally skipped this part, although you're right on publishers side, I do think there's cultural aspect too, cause even if it's uploaded for free many mangaka and artists get really pissy if their stuff is uploaded somewhere else.
And before someone say anything, it's not the same as in the west lol, western artists of course also get pissed, but they know that's how internet rolls, I've seem Japanese artist get pissy and surprised that it happened at all, as if they never thought it was possible.
So even if you ignore sales, laws and whatever, many would still be completely against what we do out of principle due to different cultural values.