Why only 6.2 percent of American citizens own Bitcoin?

According to this article , only 6.2% of a highly developed country like the US of America own Bitcoin , which seems unreasonable among the crypto community who rely on the Americans for Bitcoin to be mass adopted quite fast around the world. Here is the link of the news:
https://www.tronweekly.com/bitcoin-advisory-founder-shares-research-that-shows-6-2-percent-of-american-citizens-own-bitcoin/