it's often seen as kinda just being a bad person. this bad thing that doesn't make sense and isn't in one's self-interest, and people should just stop doing it.
but i thought of a reason it'd happen and way it makes sense. i think this helps explain it.
my theory is people chronically fail to get their preferences met, especially longer term ones. when they try to plan ahead, it doesn't work. this is due to lack of skill. eventually, after many failures, they stop trusting their ability to get good things later. they stop having any confidence that planning for the future will end up working out well.
so they try to get short term preferences met. because it's the only way they get preferences met at all. due to lack of skill.
given the context, being short sighted makes sense. if u only have the skill to get short range preferences met, it makes sense to pursue them and not pursue other types of preferences you're not able to succeed with.
just trying to think more long term wouldn't solve this problem. it wouldn't make them have skill. so the standard advice people get about being short sighted won't work. what's really needed is to improve their skill at managing longer term projects. they need to gradually build up the ability to plan further ahead successfully.
building it up by working on slightly longer range preferences is one of the ways to work on this. keep increasing the time a little bit. plan 20min ahead. then 25min. then 30min. etc. get a track record of success and confidence, and build up the time to longer times. this isn't a full solution though. some of the problems will be related to specific topics, not the amount of time involved.
Edit: added text emphasizing lack of skill point.