What does a politician who advances to the point of being able to make decisive choices most favour? Getting their policies across? Yes, but I would argue generally by the time politician makes it to a place where they can enact their policies, they might have one or two they're willing to risk losing that power for -- if you're lucky! Generally enacting good decisions comes second to ensuring you'll get back in next time.

If a politician highly values re-election, and retaining power, then voting on the basis of intelligence, rationality, etc is unlikely to result in the best decisions being made policy wise. Instead it is likely to result in the best decisions being made to increase that politician's popularity, or otherwise result in the greatest chance of re-election. In this case, intelligence and rationality can easily become tools that actually distort that politician from making good policy decisions, because he or she can easily see the outcome of them.

For example, take a look at drug policy. To ther best of my knowledge, all evidence points that illegalising substances does little to reduce their use, and instead wastes taxpayer money, increases the power of organised crime and increases harm to those who choose to use illegalised substances. None of these outcomes are desirable, but poor drug policy persists. Why? Because it would cost a lot of political capital to address, results would take time to filter through, and your political rivals can hit you hard with populist nonsense in the mean time which will weaken your position electorally. Any intelligent person who values their own re-election is probably not going to risk implementing such a policy, even if all other considerations aside they thought it was for the best.