Because that listing is probably a scam!
If a rent seems too good to be true - it usually isn't true!
The scammers use real listings, cut and paste the photos and create fake listings.
They put extremely low rental prices on them to draw in hopeful tenants who think they are getting the bargain of a lifetime.
It's not bargain..........it's a fraud!
If you contact the person who claims to be the owner/landlord, they will tell you they are out of the area/country, and cannot show you the home in person (that's a big red flag).
They often have creative reasons for being away. (some claim to be missionaries ......some claim to be disabled....they can really be creative!)
The may ask you to fill out an "application: - don't do it!
Then they will ask you to WIRE MONEY to them for the keys!
DO NOT DO THAT!
Glad you questioned this before getting more involved.
You might want to click on "flag" under the listing and report it to Trulia as fraudulent so they can remove it.