1) I do so because there is nothing to win. That is like getting checkmated in a game of chess and claiming to have "won" the total number of pieces still left on the board at the end of the game. That isn't how the game works. The game is the electoral college, and as I have written before, we don't know how the popular vote tally would have turned out if the election had been run under that rule.
2) Democrats' fascination with watching Clinton's lead grow is wallowing in misery for no reason, particularly given 1.
3) Back in the "Nate Silver is full of shit" series, I excoriated Silver for emphasizing the possibility of a popular vote-electoral college split, and thus overestimating Trump's chances, when Clinton's popular vote lead was around 5.5 points. Hey, look! When her lead is just over 1 percentage point, it is possible. It is still hard to say how much of that was Comey's meddling and how much of that was widespread polling error, but my basic point remains true: popular vote-electoral college splits require close elections, like around 1 percentage point in the popular vote. Will Clinton's lead get high enough for that to change as the last few numbers come in? Nope. Not even close.
4) Legitimacy is about perception. Trump won given the rules of the game, and he will be perceived as legitimate by the majority of the populace. Trying to fight that by pushing the popular vote is a losing game.