It's not at all that simple. The next candidate is then, during the election, free to position themselves however they want on the issue, whereas the President

It's not at all that simple. The next candidate is then, during the election, free to position themselves however they want on the issue, whereas the President who chose to circumvent Congress and unilaterally implement a policy would be a much riper opportunity for attack in the next election cycle. Liberal Democrats can then feel better (via recency bias) about a party that continued the Patriot Act, Gitmo, whistleblower prosecution, etc ad nauseam, while the next candidate can appeal to the moderate right that "hey, that was the last guy." My point though was that it would be a misconception that an outgoing second term President doesn't have to weigh the impact of their decisions on future elections, even if they themselves will never run in one again. They aren't truly free to just drop whatever policies they want with no consideration for how it will impact future elections. This one is getting done precisely because it can work with that agenda, unlike other possible policies that I'd bet, deep down inside, he has to know would also be good for the country - e.g. rescheduling marijuana or ending the war on drugs - but that would have a larger negative impact on future Democratic candidates.