It can be a multitude of reasons:

Deflation is better than inflation
It is better to have a decentralized power
Transactions in Bitcoin are cheaper, easier in a digital world
The Blockchain: a PUBLIC record of every transaction
I hate Ben Bernanke or the Federal Reserve System
The security of Bitcoin's cryptography
Irreversible transactions
A new economy to start a bushiness in
Anonymity (if done properly)
Dude, I can buy drugs like I buy shit on Amazon... awesome
I don't know, my friend uses it and I just follow whatever they does cause I think they're cool (majority of people)
I like code
I like turtle
Miner: "Free money man!"
we can win a major battle in the arms race and gain a new territory of freedom for several years
Etc...