Also, if your neighbors see someone throw a brick through your front door they will probably call the police. If they see a person "delivering a package" they won't.

Anecdote, but two weekends ago my apartment was broken into twice in the same weekend. The first time nothing was taken, the second time they took a bottle of display scotch (read: just tea inside) and some loose change. The first time they jimmied open a window, the second time they physically broke a glass window to reach inside and open the lock.

Note, neighbours don't generally give two shits about break-ins, unless you have neighbours that are also actively engaged in the community. (Also never underestimate the apathy of others).

All a lock can do is slow someone down. If they want to get access to your home, they will. I agree with you that locking your front door is always a good idea, and certainly in some situations a thief will want to employ a lot more stealth with their actions. But there's also thieves that are up to their eyeballs on drugs and that shiny thing on your counter top is all that they care about.

And get a pay-out on insurance.

If there are signs of forcible entry then my policy says I'm covered. If I left a door unlocked then I'm on my own.