-I think It is popular. many people accepted trade in Bitcoin because It is recognized and accepted as a currency by many.
-Bitcoin is decentralized and limited. This is a major factor for many Bitcoin users. Bitcoin is hard for governments to trace and tax
-Bitcoin acts like an equity investment. The market value of Bitcoins has had wild swings in value and even a market cap.
-Bitcoin is a social network. The Bitcoin "community" is active and acts like other online social networks.
-There are only 21 million bits so it has the same value as gold.
I think it is not about popularity, being decentralized and limited, an equity investment, and social network. The value of bitcoin doesn't rely on the mentions above but I think it is all because of the unique characteristics of bitcoin to manage the digital currency in our world as we are all people who are oriented about gadgets.