Why is the hash rate pumped near difficulty calculations? My question concerns Litecoin, but could apply to any other cryptocurrency.

I was inspecting the Litecoin difficulty chart and saw a pattern that seems to occur regularly: a dip in the hash rate just before a retarget, then a large, artifical pump to set the difficulty higher than it "should be". An example:



Why would miners do this? For maximum profitability, shouldn't miners attempt to keep the difficulty as low as possible? Additionally, why the regular dip just before a retarget?
It's more likely either a quirk of the difficulty calculation, or just coincidence. There's no reason, and indeed no way someone would make spikes like that, short of having massive amounts of reserve hashing power for the opportunity. There's no positive or negative of this sort of behaviour, so it's hard to believe anybody would.