Essentially it gives you something structure focus/behavior around so you can stay busy and sort of order your life a little more like. A guy who has no prospect or puts 0 effort in to date will only kind of consume media or maybe he has hobbies but be very self contained.
If that person starts simping they can then associate different things they do with that person they are simping after. It can be motivation for working more, getting into hobbies, being healthy.
The sort of phenomenology would be say you have a drinking problem, apart from simping you have the normal reasons why not to drink but with the addition of simping the ideal of this person "colors" everything and just gives you something very clear and explicit to redirect your focus, and remind you of what you should be doing such that you were to hypothetically end up with them (or someone like them).
I think if you want to present it fairer you could present simping being engaging with that person as a type, not that you expect to have a relationship with that person in particular but it makes the possibility of "that type of person" being someone you could be in a relationship with a live option again. Might help motivate someone to go out more and sort of re-engage with society if they are a bit of a shut-in.
It recontextualizes the things you do and can direct you to better things you might not otherwise consider in the stupor you typically live your life. Stuff to look forward to, think about etc. Gives it some structure even if it's a larp.
Waifu stuff is also pretty similar but it happens differently. Even just basic stuff like "it gives you something to use as a desktop wallpaper" or something. Or maybe explore personality theory and why you like that particular character.
It can also be used to just distract you from your problems/what you need to do in the negative manifestations that go more negative. welcome to the nhk presents the psychology of that well i think.