That really depends on the location these people are working from. In most of the world, those are insanely high salaries.
A company like this doesn't need to be based in SV.
Why didn't this start from say Mexico? Or Singapore or Vietnam? Or at least Germany which has a good record of freedom conscious tech scene .
My bet is in something related to the "maslow pyramid": people in SV have so much money that have everything solved in their lives, so they have the luxury of spending their time in this sort of problems.
• Telegram - Founded: Russia, Headquartered: Dubai, Users: 500M+
• WeChat - Founded: China, Headquartered: Shenzhen, Users: 1.2B+
• LINE - Founded: Japan, Headquartered: Tokyo, Users: 84M (Japan)
• Viber - Founded: Israel, Headquartered: Luxembourg, Users: 1B+
• KakaoTalk - Founded: South Korea, Headquartered: Jeju City, Users: 52M+
• Zalo - Founded: Vietnam, Headquartered: Ho Chi Minh City, Users: 100M+
• ICQ - Founded: Israel, Headquartered: Cyprus, used to have big market share
• Skype - Founded: Estonia, Headquartered: Luxembourg/USA, Users: 40M daily
2. It's probably a matter of Venture capitalists. Even if you aren't from SV, you may strive to go there to get funding for a pitch or find talent. Similar to your prospective actor that moves to Hollywood. Go where the crowds are.
Now, we can ponder why SV became a tech hub, but current market forces makes it ripe for tech startups.