Why people should use bitcoin, because it is easy to send and receive money from all over the world, no need for iban no need to pay additional fees to the bank so it made our life easier.
Bitcoin is relatively new form of currency. People should use bitcoins because the transactions are made very fast, cheap and is highly secured you don't need to trust anyone else. you will have your own control on your money.
I disagree about the "cheap" term that you have used, because using bitcoin is not cheap, I mean even the transaction fee is not like that way it is before, it is too expensive to most of the users here in this forum, so I guess using the term "cheap" is not appropriate. If you are saying that it is cheap because you could buy things easily in a small amount compare if you are going to buy it through fiat, then I guess you do have a point, but still it is not a good thing to do.
Spending bitcoin on every transactions that you are going to have in your everyday lives for example is just a waste of profits that you could make out of it if you are going to hold it in the long run.