According to BlockBeats news on July 23, crypto KOL darkpools analyzed on social media that the recent queue of 620,000 ETH for unstaking may be due to:

Giant whales withdrew ETH deposits from Aave (reducing ETH supply), leading to a surge in the utilization rate of ETH on Aave, which caused a significant increase in ETH borrowing rates; users employing stETH for looping became unprofitable due to high costs and began to deleverage; a large amount of deleveraged stETH entered the staking withdrawal queue; some users chose to directly sell stETH to avoid the withdrawal queue, resulting in stETH being unpegged by 30 basis points (0.3%). The remaining loopers face a dilemma: either accept the 30 basis point discount (which translates to a 3% loss under 10x leverage) or continue holding and incur interest losses until stETH regains its peg.

Because the oracle price of stETH is based on the redemption value rather than the market price, lenders are currently stuck in positions and may have to wait up to about 18 days — this is the current ETH unstaking queue time. If the situation continues to worsen, there may also be liquidations triggered by the accumulation of interest on stETH, which will further undermine the peg of stETH and exacerbate the situation.