That's a big overgeneralisation. Scientists can often be seeking to further their own agenda and politicians can often be trying to legitimately improve things. At the end of the day most examples of both are really driven by some form of furthering their career. Scientists usually need funding which can be difficult to come across if you're doing the "wrong" things. Politicians usually need votes and campaign contributions which can be difficult to come across if you're doing the "wrong" things.

That said, at the end of the day scientists win when they can make statistically viable predictions and politicians win when people like what they've done so it's not as if they're exactly the same. But the engineer-type tendency to reduce this to your simple one-liner hurts far more than it helps.