Bitcoin is very popular because a lot of people talk about bitcoin, when there is not much talk like in 2010 the price will be cheap and it will never be this expensive, but when a lot of people talk about it then the price can soar and make the bitcoin price even more expensive.
Of course, there are several reasons for the current popularity of Bitcoin. First of all, because bitcoin was the first and only cryptocurrency for a long time, for many, when mentioning cryptocurrency, the association occurs primarily with bitcoin. The second, and in my opinion, the most important reason is that it is generally believed that bitcoin will grow in price for a very long time. People expect to make a high profit, and therefore they buy it and hold it.
I remember when the results of a survey were released where bitcoin holders were asked if they would invest in bitcoin if it stalled in price. Most answered in the negative.