Because it is just a Bitcoin Legend! (This is about that if laszlo don't buy the pizza and keep the coins till the greatest price, he would get $10 million!)
Don't you get it? This is an historic thread because if Laszlo hadn't broken the deadlock and actually started SPENDING Bitcoin in transactions for something with intrinsic value, then Bitcoin would have remained some kind of 'imaginary nerd money' that never actually made contact with the real market of goods and services and, you know, acquired any market value in the first place.
If Laszlo hadn't spent 20K BTC on pizza, and nobody else had broken the deadlock by doing something like it, then BTC right now would not have any value whatsoever.