One piece tops exist. They are rare, but like many things in guitar it’s been done. While quartered 2-piece tops are most common today, 3 and 4 piece tops were more common a century or more ago. I don’t know the reason. I suspect that it simply is because it’s easier now to globally source and transport wood, whereas in the past people had to rely on local sources or a scarce few known suppliers that had limited geographic range. I doubt Torres had a philosophy about 3 piece tops, although our only resources that provide insight are limited (e.g., Romanillos).
"Life is under no obligation to give us what we expect" - Margaret Mitchell