Why does market's get so volatile on Expiries

There is a popular belief that market mainly remian sideways on expiry day, but for last few weeks market’s are going wild on expiry. Is there any specific reason for that?

Positions in Options market and low theta (juice) which makes lucrative for options buyers in bulk , India VIX is good indicator of Wild moves

I see, but here i am talking about the unusual moves on expiry.
For example.
On 4 Feb 2021 BankNifty gap down 200 points and travelled down 300 points more which means early morning it was trading around -500 points, then by the 11am it went back to opening price and gave a breakout towards upside and started trading +100 points. And at the end of the day it was 500+ points.

So technically the market moved within 1000+ range, which should be unsual for expiry.

The same happened on the 28 and 21st January expiry.

Why this volatility for last few Expiries?