To protect your own ego any explanation is good enough.
When a person holds on to Bitcoin for more than a year before selling, it will only be liable for what the IRS refers to as long-term capital gains. The rate for this kind of tax is significantly lower from about 15 to 23.8%. So your logic is not logical.
They should just hold for over 1 year. It would be cheaper to pay a lower rate then to pay more taxes now. The problem is however that, at the actual rate of crashing, they will lose more money, as the IRS wants $$$ not BTC.
"Bitcoin millionaires" knew already since 2014 that they would be taxed, so why wait till end of 2018 to prepare selling coins for tax reasons. In hindsight it was a horribly wrong decision.
Probably the crash is caused by people who cannot longer suffer their huge losses and decide to sell what is left. There are far more people who lost money then people who made money.