When you clean it, you clean off the 'coating' that builds up in the neck. It usually takes a good 24 + hours for the (saltwater) bubbles to recoat the neck and make it all the way to the top again. To see what I am talking about, next time you clean your skimmer (About once a quarter here) place it in your sink full of fresh water and crank it up. (Watch that you have the overflow pointed where you want it) You will notice that it does not bubble in the neck like salt water. Point is, cleaning is good an a *must* according to all mfg's maint manuals if you want to keep it performing a peak levels. It will eventually slime over and perform again less something is broke. Sure its a pain, but if skimmer setup/maint was plug and play, there would be about a million less questions in this forum.
**As a note, I have read in some manuals that cleaning the collection cup (necK) with warm (very warm) water helps skimming restart faster. This has been my experience and if Im in a hurry, I will use a good warm, almost hot tap water to warm the collection cup up with. You can also try dipping the whole thing in your sump, thereby coating the neck with saltwater again which will shave some time off re skimming as well. Personally Ive never been in such a hurry to start skimming again, I couldn't wait a couple days, but hey, thats just me!
To fail to plan is to plan to fail.