Bitcoin price will drop with time due to transfer time, which can now can be up to 3 or 4 days, with average fee 0.0002 BTC. Therefore people will switch to altcoins, which are much more fast, and Bitcoin price will drop, altcoin price will go up. Bitcoin Cash transfer for example take 20 minutes, Doge  - 10 minutes. So this is time to sell your Bitcoins !!!
Another reason will be - large miner farms mine Bitcoins, but Bitcoin user group is the same and not expanding, so Bitcoins just loose its value due to large scale mining too.