If they had switched to FIAT in 2014 they would be paying the taxes for those porfits now in 2015. This gives them options and room to maneuver for more profits with their holdings.
And this is especially BIG deal in countries where income taxation is very high.
This is actually a credible story because of Mtgox. Since the settlement is likely to happen this year and produce large losses for some, those who lost a lot at gox but still had large gains they were looking to cash out had an incentive to wait until 2015 so that the gains and losses cancel each other. If they had sold for a large gain in 2014 and then had a large capital loss in 2015, they couldn't pair them off and the large capital loss is almost useless (you can only claim up to $3000 of capital losses against your ordinary income).