As part of our commitment to supporting the growth and operational capabilities of Mastodon, we have established a 501(c)(3) non-profit entity in the United States aimed at facilitating our efforts, including being able to receive tax-deductible U.S. donations.
It is.
The people in charge of maintaining Mastodon in particular though need to establish some kind of legal entity and that needs legal recognition somewhere.
Why? Bitcoin does not and that is the point. If there is a throat to chock some will chock it or take it over.