Locks won't stop somebody who wants to get inside no matter what. They will stop somebody who would not mind casing the house, waiting till it's empty, entering without attracting any attention and walking out with loot, which is a "safer" crime than knocking down the door or breaking a window. Breaking and entering is a crime by itself, carries minimum sentence in some jurisdictions. As I understand it's because it's hard to convict somebody who walked in, took stuff and sold it for anything other than trespassing. How do you prove they stole the missing items unless you catch them in the act or have video surveillance inside?

It's only a poor strategy in places where people lock their doors all the time.

If people lock their doors all the time, burglars probably prefer to avoid the houses with unlocked doors (because they are more likely to be occupied houses).