The reason why you put a hole in the middle of a burger patty is to prevent the burger patty from puffing up and contracting into a dome shape while it cooks.
As the heat when cooking the burger patty causes the outer meat of the burger patty to contract and shrink and the center bulges.
A 1/2 inch indentation also helps the burger patty to cook much more evenly, remain flat and keep it's consistent shape.
Putting a thumbprint in the middle of the burger patty also prevents the hamburger from puffing up and bulging in the middle while you cook the hamburger.
As the hamburger meat cooks and shrinks, the thumbprint technique in the center of the hamburger meat, helps the hamburger to retain a flat and uniform shape, which also ensures even cooking and also a better fit for the hamburger bun.
Basically as the edges of the hamburger patty cook and tighten, the center of the meat often will force itself upwards and the thumbprint indentation will counteract this.
And a flat hamburger patty also ensures that the middle also cooks at the same rate as the edges.
Restaurants get their burgers so juicy by using meat with high fat meat blends which is usually 80/20 to 70/30 chuck as well as cooking the burgers on seasoned and extremely hot flat top grills to get a fast sear and they also rest the meat after cooking.
Restaurants use ground beef with 20 percent to 30 percent fat, which ensures that the burgers retain moisture and flavor and restaurants often use custom blends of meat like short rib and brisket and they avoid overworking the hamburger patty, and never press down on the burger while cooking, which prevents losing internal moisture.
Some restaurants may press down on the burger when cooking, although others don't.
Restaurant and diner burgers taste different mainly because diners use hamburger meat that has a high fat content of 80/20 meat blends.
Diners and restaurants also use a seasoned flat top griddle as well as high heat cooking techniques to create a nice savory crust.
The diner and restaurant burgers also often feature freshly ground beef as well as the use of specialized seasoning and toasting the hamburger buns in butter or even beef tallow, which provides a richer and more indulgent flavor when compared to the home cooked burgers.
Cooking on a griddle that is seasoned, allows the fat from the other burgers that were previously cooked to also baste the current burgers being cooked, which adds a deep and savory flavor.
Chefs in diners and restaurants also heavily season the hamburger patty using salt and pepper just before they cook the burger.
Diners and restaurants often use beef that has at least 20 to 30 percent of fat, which remains juicier, more tender and also provides a stronger and richer flavor.
And instead of using standard ground beef, many diners and restaurants also use a mix of cuts of meat like chuck, brisket or short rib to get a superior taste and texture.
Also many diners and restaurants also smash the hamburger patty on the hot surface of the griddle, which creates a Maillard reaction, which is a chemical reaction between the amino acids and reducing sugars, which helps produce a crispy and caramelized crust while also locking the juices into the meat.
And using butter or even animal fat like Tallow on the griddle and on the hamburger buns also add some extra layers of flavor and indulgents.
Diners also often will use fresh and soft and toasted hamburger buns, which is combined with precise and simple toppings for the burgers to enhance instead of overpower the hamburger meat.
To make your burgers at home taste better you can also add herbs, cheese or Worcestershire sauce.
You can also add some Jalapeno peppers to your burger or hot sauce and or add some toppings like fried eggs, chips, bacon, bacon jam, sauteed onions, sauteed mushrooms, caramelized onions, avocados, blue cheese or even grilled pineapple.
Some other good sauces to add to your burger are truffle aioli, sriracha may, aioli, chipotle mayo and you can also toast the bun or use different breads.
Crispy bacon, tangy pickles, garlic butter, rosemary, thyme herbs, BBQ sauce, cheddar cheese, feta cheese, cream cheese pepperjack cheese and even garlic can all help to pimp your burger and make the burger more enjoyable.