Why people interest in bitcoin??

It is simply because of the reason that Bitcoin is profitable amongst people and users. Money is involved that will surely catch the attention and interest of people. There are lots of ways to earn Bitcoin such as through investments, mining, trading, joining signature and bounty campaigns etc. There are ways that doesn't need investment and capitals, one good example is campaigns. It will just take time for you to earn because you'll wait for the campaign to end to earn your reward.