Why do all my keys get crunchy at the same time and then get better?

Every now and then, most of the keys (50% or more) on my MacBook Air will feel "crunchy" or "stuck" when I press them. I try all the remedies like using compressed air to dislodge any debris or wiping the keys with isopropyl alcohol. None of the remedies have an immediate effect, but the problem always goes away after 1-2 days

I was wondering what is causing this occurrence. I would understand if it's debris repeatedly lodging/dislodging itself under a specific key, but it's odd that several keys are affected at the same time and then magically resolve themselves.