Tesla CEO Elon Musk, an avid Twitter user, posed a question for his 62 million followers in early November: Should he sell 10% of his stock in the electric carmaker?

The CEO, who's also chief executive of SpaceX, proceeded to unload over $9 billion in Tesla stock that month and sold an additional $963 million in Tesla shares this week. The stock has fallen about 18% since Nov. 4, the week before Musk began his relentless sell-off.

While it might be unusual to poll Twitter followers about stock sales, Musk is just one of many CEOs or founders who has dumped mega-chunks of stock recently. Those insiders included Microsoft's Satya Nadella, a much more conventional CEO than Musk, who sold a whopping half of his shares last month.

The Wall Street Journal on Thursday reported that insiders like Musk and Nadella sold a record $63.5 billion in stock so far this year — a 50% increase from all of 2021. Why the surge? Three main factors have contributed to the sell-offs, according to Daniel Taylor, an associate professor of marketing at the University of Pennsylvania's Wharton Business School. Those include the contrarian tendency of insiders sell when the market is high; inflation; and pending tax legislation.

"Put all those things together, and you get this record selling," Taylor told Yahoo Finance Live on Friday.

While Wall Street was rattled on Black Friday by fears of a new COVID-19 surge, the market hit record highs earlier in November and shook off concerns over the new variant relatively quickly. And insiders like to sell stock when the market is hot, Taylor noted, pointing to sell-offs right before the internet and housing bubbles burst. Indeed, hedge fund manager Michael Burry, who correctly predicted the 2008 crisis, sold most of his U.S. holdings in the third quarter of 2021 as the market soared, as MoneyWise noted.

"You see selling at peaks and buying at dips, so if the market is peaking, we might see increased insider selling," Taylor said on Friday. "But in addition to that, we also have record inflation. So if you're thinking about where to put your money, you want to make sure you're not going to lose any purchasing power."

Of course, many people also don't want to lose money to taxes either. Insiders may be unloading stock in anticipation of President Joe Biden's Build Back Better Bill, which passed in the House of Representatives last month and now awaits a Senate vote. That bill proposes almost $2 trillion in tax hikes on corporations and the wealthy, as The New York Times reported. It also includes a tax on unrealized capital gains, meaning investors would have to pay taxes on money they made from stocks even if they didn't sell them.