I think one of the biggest factors is how strict they are when it comes to KYC enforcement. Exchanges mostly grow big if the KYC requirements are relaxed. Remember Bitmex before KYC. It was so huge!
Once Bitmex started mandatory KYC verification, most of the derivatives trading volumes moved to Bybit as so on

I don't know much about Bitget's KYC requirements, but I believe it's one of the reasons the exchange has grown exponentially.