maybe because of the large number of people who adopted bitcoin yesterday that made the price of bitcoin quickly experience a good increase. because the impact is enormous for the increase in bitcoin if there are many people who adopt bitcoin on a large scale
I think this is the long term cause of Bitcoin gaining but I don't think this is the reason why Bitcoin triggered sudden rise. There are a lot of factors such as SEC released guidelines for token issuers, Elon Musk's support to Dogecoin, & etc. We can't exactly tell which of these factor contributes BTC's gain but what important is that we see how people really value cryptocurrency, Bitcoin, and Blockchain.