European swords tended to have fewer impurities. Europe had better iron and superior steelmaking. They did not need to fold the blades and as a result, they could produce monosteel martensite blades in large quantities. With the copious water power giving them access to powered hammers and grinders, they could mass produce quality blades. Indeed, in Renaissance England, even workmen could afford a good sword.
Folding steel is needed to even out the carbon content in steel. But it can structurally weaken the blade because the welds between layers are imperfect, allowing microscopic impurities, inclusions and such. When the japanese smiths had access to good steel they would often forgo the laborious folding process. of course, it was still done for the most exquisite blades because the results are gorgeous (similar to the reason Europeans kept using pattern welding...twisting bars of iron together long after they no longer needed to).
What I have always liked about the Japanese though is that they continued to maintain their blades. Some of those Koto from the sengoku jidai period are still stunning to look at.
The europeans simply put them into storage and they degraded over time.