I, too, wish that Coinbase would figure out better planning in order that they do NOT run out of coins...
If the price is falling fast, it would be stupid for them to buy lots of BTC beforehand just to be able to sell to people with no delay over the next few days. The loss could easily wipe out all that they make from fees, and more. Better leave the clients waiting.
I believe that is Coinbase's current business decision, in order to NOT be over exposed to downside volatility - however, it may be possible for CB to figure out ways to automatically buy the needed coins on the exchange, at the same time that the customer buys the coin, in circumstances in which they run out of coins. I don't know the exact solution, but I do agree with you that their business decision is to not over expose themselves to downward BTC price volatility.
The problem I'm having with Coinbase is now they want to control volatility on
both sides of the equation: during sharp downturns and sharp upturns. So this means that they will quickly and mysteriously "run out of coins" during the next bubble as well, which will neuter how high it can go by excluding their customers' influence on the market. This is not allowing the free market play out appropriately, it is trying to
control the market, and that is what worries me about Coinbase.
You are reading wwwwaaaaayyy to much into the situation regarding their control or attempt to control the market. Their business model is based on transacting coins, and their price between buy and sell is fairly low. Sometimes the price does NOT update quickly enough and sometimes the price gap is bigger on purpose (I think that their software does that to protect themselves from volatility).
Don't get me wrong, I have outright accused them of manipulation in writing, and they responded to me and I did NOT buy completely their explanation. NONETHELESS, they are NOT involved in manipulation at any level near what you are implying and what others have also implied. The facts just do NOT add up to that.