Not only does that make more sense because of the island size like you said, but the size fits between a minecart and a regular train so it's still plenty large enough to transport players, materials, and animals. It would also simplify the amount of track pieces, etc. because you're not doing different sizes for full sized trains, minecart, etc.
could still build small bridges in something like a small cluster of islands. keeping trains to a chain of islands gives ships a purpose as well.