Why do we slice some meats thinly and not others?

Some meats are sliced thinly to break up the muscle fibers that run through it. A properly sliced flank steak is tender, while unsliced or improperly sliced it's tough and chewy.

Not all cuts of meat require the slicing, however. If it doesn't have long, strong muscles, it may be fine without. And this is a function of cooking.... tougher working muscles can. E slow cooked until it falls apart on its own, such as for pulled pork.

Most cuts of meat from larger mammals may be sliced thickly or thinly, but the decisions soon often comes down to tradition more than anything else. There may be national or regional dishes that prepare a specific cut of meat in a specific way. Not only in how it's cut, but how it's prepared and possibly how it's presented and accompanying dishes.

When it comes to sandwiches, I'm of the opinion that shaved meat is always superior to sliced (except possibly when we're dealing with some that weren't a whole muscle to start... meatloaf, liverwurst, etc.... although salami, bologna, formed ham and many others are still better shaved). But I agree with Cindy that thick slices are often better when served on a plate. (and more convenient to turn the leftovers into a casserole)

Have you ever been to Arby's? (see Arby's Roast Beef - what cut of meat?)

The beef equivalent of a Ham is called a Steamship Round and it is commonly served roasted and, yes, sliced thin. It is the whole primal round of a cow.

For the market (in the US) the round is commonly butchered down to other, smaller, cuts. Tri-tip, rump roast, eye of round. For the most part You will only see a full steamship round at large meals or in cafeterias or a catered event.

(note: before editing the question originally contrasted ham vs. steak (presumably beef))

Any meat can be thinly sliced. How meat is sliced is usually dependent on what it's going to be used for. Some examples:

• We have a market that sells very thinly sliced ribeye steak. I will buy that if I want to use it for sandwiches or certain Mexican dishes. But, if I want to sit down to a steak dinner, I don't want paper thin meat.

• If I use ham for sandwiches or biscuits, I am usually going for pretty thinly sliced ham. But, if I want a ham steak, I don't want it paper thin.

The same goes for chicken, turkey, lamb, etc. Mostly, it comes down to the intended use.

The other factor involved is personal preference. For example, I have seen thinly sliced turkey (both processed and fresh cooked) served with the fixin's for a turkey dinner, but I personally prefer a thicker slice or a turkey part (thigh, wing, etc.). And in that case, I don't want the processed version, either.