The real issue is that there is no payoff. I can't even get myself to watch more than 10 minutes of a magic preseason game. If they are down by 20 do I really care if they are able to come back and win? If they are up by 20 is there any real excitement? The win doesn't matter, nor does the loss.
Teams aren't playing their normal line ups, teams still have players on them that won't even be on a team in the regular season who are getting minutes. It is still somewhat awesome if, for say, some rookie dunks on Lebron, but at the same token, does Lebron really care about the result here? Is it anything like when he is playing at high intensity where he would take such an act personally?
Preseason is just glorified scrimmages where coaches can try out their new tactics and ideas, where different line ups can be tried out to see if they work, where players can get themselves into game shape, and where fringe guys can make a statement on why they deserve a spot on a team.