Jeff Bezos just sold $1.8 billion worth of Amazon shares - here's our best guess at why

Executives from these companies testified before a Congressional antitrust subcommittee in July to answer questions about their business practices and whether they make it more difficult for smaller companies to compete.

Democratic senator and 2020 presidential candidate Elizabeth Warren called for regulation of big tech firms like Amazon earlier this year. Under her plan, large firms with annual global revenue of $25 billion or more would be classified as "platform utilities," and certain past acquisitions could even be reversed.

The scrutiny has prompted tech firms to defend their business practices more vocally than ever. In his annual letter to shareholders in April, Bezos didn't directly address the discussion around tech regulation. But he did stress the success that small and medium sized companies have had on his platform and referred to Amazon has a "small player" in the worldwide retail space.

Bezos liquidates $1 billion worth of Amazon stock per year to fund Blue Origin, he said when speaking at an event hosted by Business Insider parent company Axel Springer last April.

"The only way I can see to deploy this much financial resource is by converting my Amazon winnings into space travel," Bezos said at the time. "Blue Origin is expensive enough to be able to use that fortune."

Bezos may not be as much of a philanthropist as other tech giants like Bill Gates. But he does operate a charity called the Bezos Day One Fund, which funds non-profits that help homeless families and builds preschools in low-income communities. He started the fund with $2 billion, so it's possible that he may be putting some of the cash from the sale toward that project.