In all fairness, another quite possible (if not more likely) interpretation of this message is that CoinBase simply does not wish to risk the company's financial well being, by holding Bitcoins in any excess (excess defined: - an amount of something that is more than necessary, permitted, or desirable) and so they don't end up "holding a bag", as things are getting worse and worse for Bitcoin valuation. It might be their preference to "sit" mostly on cash and as far as I know, they have been having Bitcoin shortage, most of the time for the past few months, since the major downtrend from $1000's level started.

P.S. I would prefer to be wrong on this, but one has to agree, them (CoinBase) keeping saying that there is huge demand of Bitcoins from their customers, while the price keeps falling down for months now, makes very, very little sense.