You can determine statistically whether you have found a block relatively early, and conversely whether other miners are unlikely to find one soon.

So you can get a head start on the next block from the likely new head block you've found.

It only works on average of course, you might be the one wasting resources if someone else published a block while you're withholding yours, but the trick is for you to gain an edge on average.

Now what happens if everyone is doing that calculation? That's where you need to do the game theory analysis (which I haven't and don't claim to understand).