The sentence regarding tourists overlooking Hokkaido states a fact if the speaker has looked up the number of tourists and knows for sure that the other islands receive more visitors. However, from sources I have checked, it is Shikoku that is the least visited of the 4 major islands so this complicates the question response.
Explanation:
The sentence regarding the number of tourists who visit Hokkaido compared to the other Japanese islands is likely stating a fact because it is assumed the speaker has looked this up or has some experience with tourism to know that the other islands do receive more visitors. To make it an opinion, the sentence would say something like "To me, it is unfortunate that so many tourists miss the opportunity to visit Hokkaido." This is an opinion because others might think it is OK to skip a trip to Hokkaido if for some reason it is more costly or inaccessible, for example. However, the sentence appears to express some level of opinion because Hokkaido is, in fact, a popular tourist destination for hiking and scenic views, especially among domestic tourists.
