Wano isn't like The Land of Swordsmanship though, it's more like Land of Swordsmiths,
It's known as Land of Samurai but we've seen that Samurai doesn't translate to Swordsmen only,
Sword is Basic Weapon of entire OP World, it's Everywhere, alongside Rifles (Then comes other Variations of Blades & Firearms ... etc),
Knights can be associated with Swordsmen as much as Samurai for example,
It's just what each Kingdom call it's Warriors, but ultimately Majority of OP World use Swords,
Even Culturally, there are many around the World who resemble Samurai, also many who resemble Knights, many who resemble Vikings ... etc
Oda simply didn't want Zoro to have a Supreme Blade yet, that's why He didn't let any Supreme Blade be on Wano,
So what happens to those Supreme Blades out there? Obviously Oda will let them fall in the hands of those who Rule the World or almost up there (Pirate King, Yonko, Greatest Swordsman, an Admiral, Gorosei ... etc)