It's telling about the options that the poll provided - most of which are completely unrealistic. The other choices were:
Hillary Clinton - lost the primary to Obama in 2008, lost the general to Trump in 2016, widely hated, will be 77 in 2024. Not a realistic option.
AOC - arguably the most left-wing politician in national office. Not a realistic option.
Elizabeth Warren - lost the primary to Biden (and several others), will be 75 in 2024. Marginally realistic option. Honestly, I'm somewhat surprised that she polled so low, but that could easily be down to small sample size
Kamala Harris - lost the primary to Biden (and several others), not particularly liked by her own party due to her history, not doing a stellar job as VP. The only realistic candidate presented, but still unlikely given her lack of popularity
Against that competition, it's not particularly surprising that a young, attractive woman with no real political baggage and that Americans in general view pretty favorably due to her acting career and our strange obsession with the British Royal Family would come out on top.