The point of coinbase is to be a normie-friendly, trusted onramp into crypto. It has tons of direct and indirect competitors, many of which will give you better rates or more variety, but none of which have managed to market themselves into the degree of "legitimacy" that people give Coinbase. It is an exceedingly boring business IMO.
If they ever sort out ACH and card payments for the U.S., I don't see what keeps them from taking a huge bite out of Coinbase's U.S. retail customer base.