Why is the stock market normally bullish through holidays and January?

Just wondering why the stock market is usually bullish this time of year and through part of January if I'm not mistaken.

Is it true that February and March are also the worst months?

I'm 30% cash. Should I put more in until January?

I plan on moving back to 50% cash in mid January most likely.

I'm still down about 25% from aths in November 2021.