@hazyg, yes retail traders are locking in those tax losses, but...

@hazyg, yes retail traders are locking in those tax losses, but institutional traders are more concerned about their end-of-year bonuses!

It's in the latter's interests to push prices wherever they need to be to hit those bonus benchmarks. Easier said than done, of course, but it's not unusual to see "unexpected" gains at the end of the month/quarter/fiscal year that mysteriously unwind over the next few sessions. It's opaque, but the anecdotal evidence from insiders is strong.