Its easy, because bch, btcsv btc gold btc diamond etc arent btc. As a store of value people and enterprises.loves btc thats why this altcoins that arent trx or eth or xmr so on...will remain  on a secondary plane. People likes to do 2 thing. Invest on the  btc, invest on new projects or invest in something they find sense.
So why i should put my money on bch when there are 3000 projects that can be more rentable than bch? And if i want a store of value...btc is the king...or i can stake dai if i prefear 0 risk...so i can do 1000 diferent things to grow my money with better possibilities.