Do you sleep better now, is that the explanation? I quit coffee for a few years, to fix my sleep, and it really did (now I'm back on caffeine and managing ok-ish).
I would suggest to anyone curious to try. And if you quit coffee make it two weeks or so to really see the difference.
I quit drinking coffee in the evening, and that helped with sleep. But sleep is also a matter of habit. If its broken, you need to fix it by breaking the current habit of sleeping schedule.
Maybe you sleep better without sleeping longer. I'm no expert, but I've read that caffeine and alcohol can affect sleep quality in that way. Either way, great that it has a good effect.
I would suggest to anyone curious to try. And if you quit coffee make it two weeks or so to really see the difference.