[Tax-chick]

"Take, for example, my neighbor, who has his home back on the market as a FSBO. Third time’s a charm, right?”

Tautologically, if the neighbor didn't price his house to sell, he didn't really want to sell it. When he wants to sell it, he will.

For buyers or sellers, there are costs and risks involved with using an agent, different ones with doing it yourself.

[DesertRhino]

Also realtors care much more about speed of sale than realizing the ultimate price if it takes longer. A bump of 20k in your final sales price will only net them an extra 600 bucks at 3%.
But to the seller, 20k extra in their pocket might be preferred.

The book Freakonomics detailed how realtors take several weeks longer to sell their personal houses than the ones they list.