So, why do we need to use Bitcoin???
simple answer , for my income for get more profit 
And that's not the only reason why we should use bitcoins because it has a lot of use that is giving us. Just like for being a currency by itself that is allowing us to transact online very fast and with cheap transaction fees. And wherever the person you need to send some bitcoins in this world he can receive it within few minutes.
This is what Bitcoin was intended to be used as, as a means of payment, to be precise. And it is not just another type of digital money, it is also a payment system in its own right. That feature alone makes Bitcoin unique and distinguishes it from previous types of money. Even fiat currencies when digitized need a separate payment system to make payments ever possible with them.
And it likes a all in all crypto currency and does have everything into it. Currency, payment processor and as well as investment. I don't know why people can't see the benefits that they can't get with bitcoin even though they already knew that there are a lot of opportunities that they will be able to experience with bitcoin.
It is an interesting question. The main reason seems to be that not so many people are using Internet to make online payments on the average. Those who do use it may be willing to at least give Bitcoin a try, but they can't easily get it. Yes, they can buy it on an exchange, but that alone might frighten a lot of people off because they would have to transfer their hard earned dollars to it which they obviously don't want to do.