As some others have already stated, this is most probably because of the price increase. The higher the price, the profitabler mining becomes.
But yeah, 21% is quite a lot.
a percentage like that is not normal and the price has stopped rising. it also coincides with multiple fork dramas and people circling who have a great incentive to usurp the original bitcoin blockchain and now is the ideal moment to attempt it.
it all seems a little too neat not to be the case to me but maybe i'm being paranoid.