WD-40 does a lot of things, unfortunately this means that it does not do any one thing well.

As a lubricant WD-40 is very thin and runny. WD-40 will lubricate for a short time, but will quickly run off. This is a side effect from it being a penetrant. If it was thicker for better lubrication it would not penetrate well.

WD-40 is a GREAT quick-fix and one-can option. I use it in that role, it gets things going long enough to let me finish the current task and get back to the shop. Once there I can get to my real penetrants (Kroil, PB Blaster) and my real lubricants (oil, white lithium) and repair the problem.

Bonus tip: wrap your WD-40 can with several turns of duct-tape. You now have two of the best quick-fix wonders in one package.