Makes sense, because laptops were competing with other laptops on the x" category, and resolution was rarely a marketing thing, especially for budget laptops. Defect rates would be based on the area (given the same density), so yields would be higher the smaller the area, but they still wanted it to be an x" display.

I also think that it may have something to do with brick and mortar stores, since they would usually play some videos on the screen at the store to show how the display looks, and having the same aspect ratio makes it look more impressive (larger image without black bars) probably made these laptops sell more.