Why Are Some Coinbase Pro Pairs Allow “Limit Only?”
I assume that the market orders are done via other parts of Coinbase, such as through Coinbase.com side (when people use the app to buy and sell), and through bots, and that Coinbase Pro users who trade by hand are just playing market maker.
That said, I’m not sure anyone aside from Coinbase themselves knows exactly what is going on.
In fact, all I have to go on is a snippet from their trading rules:
2.2 Access to Coinbase Pro and Coinbase Prime
2.21 All Traders have equal access to the Coinbase APIs and Web Interfaces. Coinbase does not provide prioritized access to any Trader.
2.22 Coinbase Market Operations has the authority to take any action deemed appropriate to preserve market integrity. Such actions include, but are not limited to, the halting of trading, modifying risk-mitigating parameters, restricting Trader access to Coinbase Pro or Coinbase Prime, restricting order types to post-only or limit only, canceling orders resting in the order book, or any other actions deemed to be in the best interest of the Exchange.
The point here isn’t that I know exactly why this is the case, it is that it is the case that some pairs are limit only (this is especially common with USDC pairs). Given this, you should make sure you aren’t waiting until the last minute to make a trade on Coinbase Pro (as it could be hard to get an order filled in a quick moving market.