The hassle of listing stuff on Craigslist or your local equivalent? Especially at the moment, a quick guaranteed transaction at a reputable place sounds a lot more appealing than having some random come over (or flake out), anguish over whether they actually want to buy or not, and maybe try to negotiate price on something you've already listed for $15.
Exactly. My wife and I are big into reuse, trying to donate, give away or sell all the things someone could use, instead of throwing them away. Experience is varied. Sometimes we do wish the process wouldn't have to involve dealing with actual people. We've been literally told to commit suicide, only because we didn't have time to make more photos of a thing freely given away, over the ones we posted on the group. Also, putting even a ridiculously small price tag on something not only doesn't scare problem people away - it brings out more of them.
The kind of people who tend to buy furniture first hand don't tend to like having to interact with the kind of people who tend to buy furniture (let alone cheap furniture) second hand if you catch my drift.
With very rare exceptions, I can't be bothered selling used stuff these days. I'd much rather just put something out for someone to take away or take a reduced amount for a no-hassle transaction like selling to Amazon.