Bitcoin vs Bitcoin Cash

I recently listened to a pair of BTC maximalists talking about how Bitcoin is the greatest thing ever, all other coins are shitcoins and fiat is the root of all evil. I could believe it. The thing is, I can't for the life of me understand why BTC is fundamentally special. If I spin up my own truly decentralized proof-of-work chain that I truly don't control why is that "fundamentally" worthless while BTC remains the greatest thig ever? Asked another way, why is BTC the greatest thing ever but BCH is a shit coin.