There are lots of reasons for the price rise of bitcoin.
Some of the reasons I can tell you.
First thing you know that crypto currency has started with bitcoin.

And as you know, the price of the crypto currency depends on the demand and the supply.

And the supply of bitcoin is low and the demand is high and there is One more important reason is acceptance of the bidcoin.

As far as the ALT coins are coming from their trading bitcoin, due to which the rate of bitcoin will remain high.