Because bitcoin is the first cryptocurrency that have been develop to introduce in the world of cryptocurrencies. Etherium and other altcoins existed because of bitcoin, simply without bitcoin there are no crypto now. A lot of people now change their life because of bitcoin which is most profitable than gold.
That's clear and I really support what you're saying because I myself also felt the change in my life after knowing Bitcoin in 2017, and this certainly cannot be denied by others and must also be acknowledged by many people that Bitcoin is really profitable.