I would not totally reject the theory about the seasons,it definitely affects people in many ways.Let's say that the winter is maybe time when people spend a lot of time in the indoors,and accordingly to that spend more time on computers/internet-but in the winter in the northern hemisphere we see that it is always the toughest part of the year for cryptocurrency.So it might be connected with Christmas-New Year holidays when people typically spend most of money in the year,and sell crypto for fiat.
On the other side at the end of the summer and early autumn people start to buy BTC just because have somewhere in the subconscious they could profit in few months and have more money for the holidays.Between all this is the summer and long-awaited annual vacations,time in the year when most people leave BTC for some time.
I can tell for myself that I'm much more active online in the winter,but how come the warmer weather I spend more and more time outdoors and I assume it is similar to most people(at least for those who have seasons).
Would winter also have an effect on mining, and the fact that miners are able to earn more in that season?
It can affect the miners in a way that they usually profit more from fees in that time,we see that increase of transactions increases the fees also.Last year fees are go so high that it was not profitable at all to send small amount of
BTC.So that time of year is very lucrative for miners,but now when SegWit is more and more accepted,and Lightning Network is becoming closer to the wider use I think that miners should not have feast of fees anymore.The only way to check it out is to repeat the situation similar to the previous year.