That's supposed to make it easier to push the meat out of the can, and to slice it neatly as you do so.
Having said that my first Saturday job as a teenager was working in the local dairy shop. It sold everything from milk and cheese to cold meats. The corned beef came in huge great rectangular cans and getting the meat out of them neatly was an effort and a half. I think the block must have weighed about 5lbs, so well over 2kgs. Getting them up onto the slicer was another effort too. Slippy things even with greaseproof folded round them.
Chicken came in huge round tins, like triple sized Pringles cans, but gammon and 'luncheon' meat came in the same kind of shape as the corned beef.
Thinking on it, all those years ago, we didn't keep the meats separate, the same slicer was in use all day long. Lethal thing, no guard, but it was the only thing the Boss cleaned himself, no one else was allowed to do so.
We sliced up the tinned stuff, the Ayrshire bacon, the roast beef, gammon on the bone, the beef ham, just as folks came in to buy. Never heard of us poisoning anyone though