I think that's one of the biggest screwups people make with WD-40 is that it's basically just a petroleum solvent and other than maybe initially unsticking things, it often makes the problem worse. As far as solvents go it's not particularly great, and in terms of lubricating or breaking free it's pretty bad. I'm surprised they still sell as much of it as they do (chalk it up to good marketing), when for basically everything there's a better choice (protip: if something is really stuck, the best tool provided you don't have dogs or children getting near is going to be acetone mixed with a good ATF).

For what it's worth, old lock grease tends to move away from where it's needed and turn into a hard, waxy substance. It's arguably better to have a lock cleaned and slightly lubricated with WD-40 than one gummed up with ancient grease and dirt, or worse, rusted.

I've heard a lot of anecdotes in every direction: only use graphite, only use a cleaning solvent. I've never read anything authoritative and I suspect the ideal approach is to regularly (e.g. every decade) disassemble the lock, clean it thoroughly, and inject grease, but nobody is going to do that.

This was in fact one of my big learning experiences in mechanical work. As a kid, my bike was running rough so i took it apart, cleaned oout all that yucky/dirty grease from the bearings using WD-40, and then reassembled it all only to find it was even worse than before. Only a few years later did I learn that wd-40 is a terrible lubricant for bike ball bearings.

You can see a similar effect with standard skate bearings used in fidget spinners - most bearings come pre-greased with a fairly high viscosity lubricant. If you spin the spinner, it will slow down quite fast, but if you take the bearing apart, clean out all the grease, and reassemble it, it will run wicked fast and long. Until some dirt gets in, at which point, grease would have worked better.