I am only playing this game the best I can in my current situation. Call me a fool but, you can’t take it all with you when you go! At the moment I hope I have enough years to spend, share, and donate what I gain here and some other strategic investments.
Part of the Biden tax plan probably will involve taking away the LT cap gains rate on income above $1M. That doesn't relate to retirement accounts but if it takes effect in 2021 it would mean that on very large LT cap gains the 20% rate would go away for those with over $1M in income, meaning that the marginal rate on LT cap gains for those with very large incomes would rise from 20% to 37% (new rate could even be higher if the highest bracket highest marginal rate increases).
Enough shares were dumped to indicate it could have been somebody selling who has more than $1M in capital gains and thinks the higher rate will come into effect in 2021.