Physical locks are for honest people. They signify that something is not meant to be accessed and at best slow down someone actively trying to access the other side of the lock.
If I can go out on a limb here, I also think I recall that they have very specific things they look for. For instance they will often run straight for the master bedroom and start pulling out drawers/checking closets because people tend to keep jewelry in there. They want small items.
Anything that slows them down tends to deter them even if they make an initial attempt
You can spudger one of the glass units out and back in from the outside, without leaving a mark.
They look better than they are.
I have heard of someone cutting through all the plastic and pulling the glass out that way, though.
Both rather more obvious that surreptitiously jiggling the obscenely crappy Eurocylinder that the door came with.
A lock forces the thief to either spend time defeating it or physically break something. Even if it doesn't slow him down it should hopefully make it visibly obvious that he's doing something illicit.
Oddly, this is a case where they would have had plenty of time to pick the lock as well, and it would have been much quieter.
People with that kind of dedication can often find gainful employment :)
Most "normal" locks don't increase the cost too much but they do raise it - perhaps enough for a thief to pick another target, or perhaps enough for the thief to choose another method of entry such as kicking in the door (which itself comes with additional risk of detection).
I have a vehicle that is extremely simple to steal (you can unlock everything with a screwdriver), to protect it I use both a pedal lock, a secret second key and a steering wheel lock.
Will it defeat a determined thief or a team of thieves? No way. However it will put off most opportunists and slow down a more experienced thief enough that they may choose another target.
I object to the word overpriced in this context. It costs a lot of money to keep locks, tools, and other spare parts in a vehicle (including the cost of the vehicle). If you need a lock now and they have one it should cost a lot more than if you need a lock in 6 months and can wait for the factory to get around to making it. When you call their locks overpriced you are failing to understand the costs and value of having a part on hand.
Maybe some of them are selling normal-price locks, but people don't call a locksmith to drill out their lock when they can borrow their neighbor's drill.
They either can't pick an easy lock or they're scamming people.