And now someone just sold 374.05139511 clams
The sell side has reduced by about that much, I'm thinking someone got tired of waiting.
I've been thinking for a while how much of a waste it is to have all those clams just sitting there when someone could have been staking them.
I expect the exchange is staking them.
In fact it wouldn't be hard to find out if you bought CLAMs from an exchange by tracing them back on the blockchain and see if they were staking before you withdrew them.
Edit: Well, OK, it looks to me very much like the exchange *isn't* staking them:

A 138 CLAM output with 22 days of age should stake very easily:
>>> 2**20 / (138.16 * 22)
345
ie. after about 345 seconds. It's inconceivable that it has been trying to stake for 22 days and not managed it.
On the one hand that does seem like a waste, but on the other hand that's better for the rest of us. Less competition, lower difficulty, more chance of winning lottery payouts.