I guess some of us just don't trust banks and governments anymore and Bitcoin and its math seems a pretty good alternative to all these official liars that rob you smiling and saying that they do it for your safety.
If anyone don't trusts banks, then when they want to get money (exchange btc), that the hell are they using? Of course banks/exchangers so I believe that's not a main reason. People are holding bitcoin to get high profit, but for that high profit there is a need of bitcoin's price rise (that usually happens). Another holding reason is to have a money for a "black day" when goverment will freeze your account and you'll get bitcoin into usd on another way.