Psychologically there's a sort of information hoarding aspect to this. I think a lot of people experience this with browser tabs, where they don't want to read something right now, but also don't want to just abandon it. So you end up with this backlog you feel you have to hold onto.
I've learned to just trust my brain more, where if something occurs to me is important, it'll probably occur to me again when its relevant, vs me treating random momentary insights like they're a priceless treasure.