Because the vote against him was split
Because people who REALLY didn't want him to win, didn't vote (like me)
Because he had a following of enough people who don't understanding that "playing the game" & "having a laugh" shouldn't be at the constant expense of someone else
Because people who liked him have the attention span of an immature flea & would think that anything approaching a mature conversation is "boring"
Because it was very, very close & may have been down to just a handful of votes & viewers who support him are more likely to vote multiple times, partly because they may have more disposable income, being generally younger & still living with parents.
Because people sometimes make very odd choices (remember "Scootch" winning the Eurovision entry slot?)
Because we didn't see half of the nasty things he said or did on the HLs programme
Because we didn't see 99% of anything remotely interesting, amusing or entertaining that the other HMs did.
Because some people would not want an Americam to win at any cost.