Not enough lookers - not enough buyers. The FSBO house has very limited market exposure, since you're limited to a few signs and an ad in the paper. Marketing is a science, it is expensive, and requires "know how".
Most buyers use a "buyer agent" because it's a free service for them (seller-you pay agent's commission), and the buyers don't have to worry about all the liabilities and disclosures involved.
Since a Real Estate transaction is a complicated process, due to lack of seller's experience, most FSBOs end up as listings.
It may take much longer than 6 months to complete the process.
But, if you can handle all the details and solve the typical closing problems, you will save thousands of dollars by not paying Realtor's commission. What you'll have to pay are only the closing costs.
Which way do you turn? To an agent with dozens of other listings to handle? Selling on your own and sweating out financing (and legal) details, lost deals, last minute closing "surprises"? Moving out, making two mortgage payments and hoping you don't get some midnight call with "bad news" about your house...