Limited supply. As fiat currencies continue losing value, as they’re designed to do, more people, particularly in developing countries with high inflation and low access to banking, will turn to bitcoin as a way out of monetary debasement and an easy way to take control of their finances. As more people ditch their fiat and buy into bitcoin, demand rises, and so does it’s price.
It’s just supply and demand. The supply is fixed in code, so we know the limited supply is a truth. Then, once you understand why there’ll be continuous growing demand, it all makes sense.