What do you mean they didn't see the usefulness of a personal boat? In many regions that usefulness is close to nothing, considering there were often limited waterways and people often lacked the funds to buy or make such a boat.

To my knowledge, regions which had swamps or many waterways, for example medieval and premodern Holland, did have personal boats, just not kayaks.

So I don't think they didn't see the usefulness, there often just wasn't any.