Also quite likely, it is due to the fact that Swedish rape law is quite different from many other countries in 2 aspects that have significant effect on statistics:

a) Every form of sex without consent is classified as rape, including "too drunk/asleep to say no" and sex within a marriage b) Every incident is recorded separately

So if a person is raped 5 times by his/her spouse, this would lead to 5 rapes in the Swedish statistics, as opposed to zero times (b/c within marriage) or 1 time (b/c same offender and victim) in many other places.

https://en.wikipedia.org/wiki/Rape_in_Sweden