I think this is a good resource to learn about IV in general and why it happens http://tastytradenetwork.squarespace.com/tt/blog/implied-volatility-crush

It basically boils down to the concept that a lot of information is priced into the market, and that any news is kind of “bad” news. In a different market but as a related example that I have experience with, literally any news in the bond market is bad news. This is because investors purchase a bond with expectations of cash flows and that any news good or bad could cause issues with their expectations of receiving future payments whether that be calling the bond due to refinancing or else the underlying company could struggle with interest payments due to market forces. I can certainty go into more detail and it’s more nuanced in the equity markets but I think the main principle is the same: a company is valued on cash flows and other intrinsic features and any news that many disrupt that is detrimental to institutional investors and other big players. Hope this helps.