The new guy won despite winning <5% of votes in the last election. If people vote for the candidate they like instead of trying to game the system by calculating who they’d rather not win the most, then maybe we can kick out corrupt incumbents and get in fresh faces (they’ll get corrupted over time too, at which point you rinse and repeat).
Instead of calculating who they hate more, the Sri Lankan people voted for the candidate they liked - an anti-corruption activist who got ~3% of the vote last time and was supported by a fringe left-wing party - and he won the presidency over the candidates of the two established parties.