There are many reasons, but put simply:

1) People have realized they can make money by releasing shitcoins. If a project has given themselves tokens before ever releasing the protocol, you should be skeptical of their motivations and their statements.

2) Bitcoin is battle tested. It has been around for over a decade, and proven resilient to government attacks and fiascos like Mt. Gox. The brightest minds have been improving it throughout that time. There is no project that compares in this respect.

3) Proof of Work. The energy and computational power dedicated to mining gives transactional finality faster than any other project. Hashrate dedicated to bitcoin dwarfs that of any other project.