What you say is about deer hunting in Sweden is true. But only for Roe deer. They are quite small deers that you are allowed to hunt with shotguns and Class 2 rifles, meaning 800j at 100m. That's typically a .222 Remington. The legality of this stands out when you take the rest of Swedish hunting laws into consideration. There reason is probably historic. There is a Swedish tradition to hunt Roe Deer these types of guns and so the lawmaker kept it.

Even though Class 2 rifles are legal it's my impression that they have become less and less popular. Most people tend to use something like a 6.5x55, .308 or 30-06 since that gives you more margin of error.

Roe deer is the also largest animal you're allowed to hunt with a Class 2 rifle. The next size deer (Fallow deer) is Class 1, meaning >2000J. You can use shotguns with slugs on boar and fallow deers, but not on Roe deer. This shows that it's not always clear how the lawmaker reasons.

Hunting laws in different countries often reflect tradition and might not always have a sound base in science. In the US you are allowed to hunt with falcons, muzzleloaders and bows. That's criminal in Sweden.