Here's some light:
1. you have to buy bitcoin with something
2. Alt research & speculation is good for BTC
3. Trading fees on all the non-bitcoin pairs subsidizes the cost of running a secure, compliant, robust bitcoin exchange. A bitcoin-fiat-only exchange would not survive
As a global order book exchange, yes. CashApp isn't global and it doesn't have an order book. It also subsidizes crypto trading with stock trading, payments, etc. Why aren't you outraged about the availability of $TSLA on CashApp?