Laura22, no offense, but allow me one little monkey wrench into your anthropomorphic FastPass analogy...
Bear in mind, since your li'l FastPass buddy can't speak, it has no idea WHEN you'll be using it, so it's waiting and waiting with no info to give the CM as to when, or even IF you'll be back later today to use it (and that's not mentioning anyone who opts to leave their li'l FastPass Buddy on line overnight, or over multiple nights, or months or even years, opting to use it "some other time").
So as the day becomes night, and attractions start getting more and more li'l FastPass buddies (name copyrighted, patent pending) waiting in the queue for their respective masters, and it's close to closing, the CMs operating any attraction has to make a judgment call. Because, at a certain point, the CM will have to close off the queue so no one on line has to be told "sorry, we won't be able to get you on before closing."
SO, the CM can either assume all those masters of the li'l FastPass Buddies will be using them today and cut off the line even sooner, potentially disappointing people who could've gone on the ride if lots of the FastPass holders DON'T return to use them...
OR the CM can assume all those old and expired FastPass holders won't be coming back, only leaving space on the "virtual" line for the non-expired FastPass holders, and let more people on the standby line...ONLY to then have a bunch of expired FastPass holders suddenly show up and demand they get to go on the ride, because after all, the time window is just a guideline! It must be true, they read it on the internet!
Not to mention anyone who has a day-old, or week-old, or however-old Fastpass who assumes the CMs will be too sleepy to notice or care.
So let's say you were the CM on that attraction in that situation, who do you tell to take off and call their Congressman if they're going to be a WATB about it: The Standby Line, who got on the line 30 minutes before closing when the sign said Standby Time was 20 minutes, but that got thrown off because of all those expires li'l FastPass buddies suddenly claiming their place in line? OR the expired li'l FastPass buddies who could've been on line during their time window but had better things to do?
Bear in mind, WDW HATES paying overtime and expects you to close the attraction on-time, even though the cutsomer is always right and should always be appeased. No pressure.
The FastPass system is not just a benefit to the WDW guest. It's a method of crowd control for the CMs. And that method is most effective when used in the manner it was designed to be used.
There may have been a time when letting people on with expired FastPasses wasn't such a big deal. After all, if someone was a few minutes late, just missed their window, they were probably on a ride that broke down, or on a bus that broke down, there was a problem with a meal that had to be sent back, bad rains closed some things down, baby had a diaper emergency, someone got stung by a bee, etc. etc., there are always valid excuses to bend the rules.
I'll even go so far as to say, IF the CMs were originally told by management to let expired FastPass holders on line, it was because WDW figured people who were late were only going to be a little late, or very late people had circumstances that were so rare and bizarre, there would be precious few people returning HOURS later trying to use an expired FastPass, and that wouldn't alter crowd control all that much.
But as the word got out that time windows weren't being watched, it's OK, you can go back ANYTIME, they don't care, that put more of a strain on the CMs trying to maintain crowd control, especially at peak times and at the end of the day when everyone is trying to get one last ride in, maybe even sacrificing seeing a parade or the fireworks to do so. And for the benefit of THOSE people, willing to miss something else to wait on that line, they shouldn't then let expired FPs be used. For the benefit of those peak times when they really need help manging crowds, observing the policy of the FP all the time is probably most beneficial to the CMs and the guests, no surprises, no mixed signals, with exceptions being on a case by case basis and at the discretion of the CMs or the managers of the attractions.
A long rant for a little issue, but there you have it...no one can accuse me of not being thorough.