Because bitcoin had already prove that they are trusted unlike other altcoin projects that are keep showing on altcoin threads with promising whitepaper but in the end it was just like others that are shit and undervalued as the time goes by. Bitcoin runs almost a decade and no scam reports are into bitcoin and the transactions are being made every second. The bitcoin revolutionized cashless payments and other altcoins will promised to do but as of now almost are dumped and being scams so people will stick on the safest crypto which is bitcoin.