What is the life expectancy of a ratchet strap?
Don't spray it with WD-40. It might lube it up enough to get it moving, but the oils in it will attract dirt and debris which will eventually lead to binding. If you want to try giving it a shot of lube, use a dry type silicone spray.

Ratchet straps are not typically a disposable item, but cheaply made straps can be easily broken. If you're handy, you might want to give fixing it a shot.  Look for things that look out of place, bent, broken, or bound up.  Sometimes the ratchet can become bound up with the strap itself, and can be fixed with a bit of yanking and cranking. Without knowing the exact type of strap you're using, it's difficult to give more accurate repair instructions.  So you'll just have to mess with it until you've fixed it, or given up. 

If you decide the strap is beyond repair, and you need to purchase a new one. Buying a higher quality strap, should insure a longer more useful product life. Just remember, higher price does not always equal higher quality.  Handle and inspect the strap in the store as much as you can. Try operating the ratchet, releasing the ratchet, tugging at the straps, etc. to try and gauge the quality.

Note:
Most ratchet straps do have the ability to destroy themselves, over tightening the ratchet can permanently damage it.