What is the Reason for increase of the Bitcoin?
Not clear you are asking about the amount of bitcoins in the market or the price ?
If you are asking about the amount then it will increase as more and more people will be mining coins. If you are asking about the price, its the demand supply ratio. The more demand something has, the more it's price will be.
yes you are right the increase of the amount of bitcoin in market is dependent on the number of miners as greater the number of miners so greater will be the amount of bitcoin in market however the price of bitcoin is depend on the numbers of users of bitcoin because when the users of bitcoin are greater then the demand of bitcoin will be increase which inturn increase the price of bitcoin and the investors are also the reason of increase in bitcoin price.