Well I recently saw an article showing that data, with charts from the last 3 years or so, and there was a dip every January, then followed by a very bullish trend. They think it could be related with people exchanging crypto for fiat, in order to buy presents and other expensive things, since it normally happens very close to Christmas and other holidays.

Not saying that this can't be true, but as the article stated, there is simply not enough that, so we can't really rush any conclusions.
Right now, there are plenty of bad news regarding crypto, and that is probably dictating this negative trend (tether possible scam, south korea regulations, exchanges hacks, etc).

As usual, crypto market reacts to fud since it's mainly composed by retail investors, and still have low liquidity. I think all of this will change in the future, and crypto, and specially bitcoin, manages to solve their problems and achieve real adoption.