Sorry, no.

I just think it makes intuitive sense to conclude that individuals who are highly self-absorbed wouldn’t necessarily care about a collective, relatively anonymous civic duty like voting.

That's very much not the same thing as the claim you actually made, which was:

people who think they’re attractive don’t vote.

And they're both deeply spurious claims to make. Self absorbed assholes absolutely still vote, their reasons for voting (likely, at least. Voter behavior models aren't super reliable) just change from social interests to personal ones.