they had just been approved and were in limited supply...but for obvious priority reasons...and to encourage those who were skeptical...Joe, very publicly, showed his trust in them.
You need to do a little research before posting...not just go with what your gut tells you...but that's only required if you're trying to convey the truth and not political "Chaff".
Link: https://www.ajmc.com/view/a-timeline-of-covid-19-vaccine-developments-in-2021