Why do labels choose the worst song to be the single?

I know the bands dont pick the singles, but why is it 95% of the time it seems the single is the worst song on the CD. For example, if all I heard from Nickelback was Photograph or How You Remind Me then I would hate them too.

It's all about money...they choose the songs that can sell. Back then, stations were an album format so if an album song came on, it could become popular.

The band KoRn was once approached on making a radio-friendly single...they responded with a song "Y'all Want A Single" which was supposed to be a 3:30 catchy song...but had too many obscenities.

They probably look at it this way; What will sell the most? Which songs will appeal to the masses?
The more "majority friendly" the track is, the more likely it is to sell.
You may think it's the worst song, but they obviously do not. It's all subjective.

they pick the song that they think will sell the best and get played the most on the radio

Ugh I know what you mean. Then we get to listen to them get over played on the radio. Of course...that's why I stopped listening to the radio. Music has gone down hill. I truly enjoyed the 90s. Smashing Pumpkins, Collective Soul, Bush, Nirvana.

It has to do with what the label thinks will gain the most popularity and make the most money.
For example "You're Not Alone" by Saosin is a good song, but certainly not the best on their CD.
The singer Cove even said it was a cheesy song and it was written at 3 in the morning.
Obviously he didn't want it to be the single, but it was since the label thought it would gain the band some recognition.
They seemed to know what they were doing. That song is being played everywhere now.

Unfortunately it comes down to the age old battle of art vs business. Clearly, the labels are in the game strictly to make money so their main objective is to always pick the song they feel will get maximum radio exposure. By virtue of that alone, you can almost always count on the single being something to match the tastes of the lowest common denominator. Labels, radio and advertisers always trend toward the conservative side, so anything different or exciting is seldom the first choice.