I thought it's because of the promise of getting rich quick. All those people who missed out on cheap Bitcoin and then created their own hype hoping to still get rich, meanwhile scamming billions of dollars from gullible "investors".

Is it? CoinMarketCap shows this Top 10:
Bitcoin: $383.5
Ethereum: $182.5B
Tether: $67.5B
USD Coin: $52.2B
BNB: $45.0B
Binance USD: $19.3B
XRP: $16.6B
Cardano: $15.3B
Solana: $11.0B
Dogecoin: $8.4B
Out of a total market cap of $968.6B, this $801.3B is 82.7% and Bitcoin is 47.9% of the Top 10.

Ethereum is centrally controlled, abandoned it's core principle the moment it was convenient for the creator, and doesn't stand for anything Bitcoin stands for. It simply doesn't count. Tether is centrally controlled and isn't even a cryptocurrency. USD Coin also. BNB and Binance USD are also centrally controlled. XRP is centrally controlled. I'm not sure about Cardano and Solana, but don't care enough to check. Dogecoin is a real cryptocurrency, even though it's a joke and hyped by the biggest troll on the internet. So let's give the last 3 the benefit of the doubt. That makes Bitcoin's market cap 91.7% of the real cryptocurrencies in the Top 10! And possibly more, since I'm not sure Cardano and Solana even qualify.