Coinbase just eaaaats into profits with it's hefty fees.
Both of them are fiat bridges, no proper exchanges unlike Gemini which is also a fiat bridge and has an active trading platform.
Gemini only supports BTC and ETH though.
Gemini does not charge fees for deposits or withdrawals and only charges .25% or less fee for trading.
Coinbase charges around 1.49% for bank transfer purchases and 3.99% for credit/debit card purchases.
Gemini is a low fees fiat bridge, cheaper than Binance SG (.6% trading fee
.0005 btc withdrawal fee) https://www.binance.sg/en/fees