Flattening doesn’t necessarily “squeeze the juice out of them” if they are flattered while still raw. Grab a hunk of raw hamburger. Now squeeze. Did you see juice come out of it? Nope. It only squeezes out the juice if it has cooked to some degree and the fat has started to melt.
Hmmm…now I’m thinking about the scientific approach to the thin-vs-thick debate.
When a burger is cooked which happens faster: the melting of the fat or the cooking of the meat?
If the meat cooks faster than the fat melts it would seem that a thinner burger that spends less time on the heat would have a better chance of being juicy than a thicker burger that takes longer to cook all the way through.