Anecdata: I cut out all caffeine during quarantine and I've never slept better. But I was drinking ~12oz a day prior to that. And I also cut out all the other drugs in my life too. And the commute due to WFH. Honestly, trying to say it was one thing that made my sleep better isn't really possible, it's all entangled. But the SO says that caffeine was the major culprit.