1. Coming out of a long bear market (the second long bear market for Bitcoin, akin to July 2011 - Jan 2013).
2. Several months after the latest "halving" (when miner rewards are cut in half). The last halving was in November 2012.
This time around very significant numbers of Bitcoin buyers are then using Bitcoin to buy altcoins... which are then being moved into other altcoins by altcoin traders. With some altcoin projects gaining major kudos the new hodlers are in altcoins. These cycles lock up Bitcoin in altcoin trading... further reducing supply in fiat markets. I think this shouldn't be underestimated.