Apparently William is so popular in this American poll because their politicians are such unstable and unreliable people. Trump is distinctly odd and Biden seems to be having major political problems.
It's one of the reasons I do support the retention of the monarchy. In an increasingly politically unstable world with politicians no one really trusts, the monarchy is great soft diplomacy and just there.
Of course it needs scrutiny and reform but with a new monarch and a solid heir, this should happen.