I mean, it could be anyone. 'Tis the season when the timeshares "for sale" go up. We've got another month or so before we flip from a buyers' market to a sellers' one, and this cyclic behavior happens ever year.
Then, layer macroeconomic forces on top of that. Inflation is unexpectedly sticky, and the chatter is not only the Fed pausing rate cuts, but whispers of rate increases. The VIX has been higher YoY, the stock market is "frothy", options volumes are going up---all signs that the market is getting nervous.
It's rarely any One Reason, even though The One Reason is a compelling story line.