I think the robot is programmed to be somewhere between bullish and bearish. So it sells gradually as the price increases and buys as the price falls. Or perhaps it's based on something more sophisticated, like calculating the rate at which the slope steepens and setting the buying minus selling rate to proportional to that (which might imply the need for such infrequent trades). As a robot cannot predict the future and shouldn't really make partial judgements about the fate of BitCoin, this makes sense.