30 million accounts don't mean they all trade on Coinbase, because I know a lot of people choose Coinbase to store their Bitcoin. As for Binance, I don't know how many accounts are available but I'm sure the volume volume on Binance is always more than Coinbase
Coinbase primarily caters to European customers and that makes the exchange always average trading volume but this can be considered the best investor protection exchange so Coinbase always has Great trust of investors. At this point Binance is dominating this market but the security of this exchange is still very poor so in the near future Binance will soon be replaced by a better exchange.