I will be wondering that why the price of BTC don't be constant , it keeps changing

I guess this must be a joke - LoL

But in case it is not, have you ever heard the word markets? That's that strange entity which happens to help discovering the prices of things...
I will be wondering that why the price of BTC don't be constant , it keeps changing

I think it has something to do with supply and demand, people sell for profit and people are buying for future profit, the law of buying low and selling high applies to this right now there are much selling at a low price.