Obama never talked about how children's IQ would be higher in the future because his administration calculated the dollar value of children's IQ's and opposed it to the costs of reduces mercury pollution.
The policy was done by the EPA with very little public debate.

On the other hand the EPA didn't get done much on global warming where there's massive media attention.

why even have elections?

To allow voters to refuse to reelect politicians with bad track records. If democracy is done right, politicians who mess up don't get reelected.

If it comes to decide whether to vote for a politician's you don't focus on what he promises for the future but what he did in the past. That provides for democratic accountability.

To choose representatives and not to choose policy.

If I look at Bernie Sanders I know that he engaged in good policy for decades. He voted against the Iraq war and the patriotic act. That tells me much more about him than any promise he makes before the election.

If, during your term, you completely neglect everything you talked about while running, you'll take a hit in the next election

Bush campaigned on "no statebuilding" and then went to do very expensive statebuilding in Iraq or Afghanistan without the Republican base complaining. The Republican didn't like Clinton's intervention against Kosovo, so it made sense for Bush to run with "no statebuilding".

Obama promised to clean up Wall Street but did nothing substantial. He engaged in busywork and passed laws but they are more symbolic than real reform.