why are the deck drains raised off the deck?

[Build6001]

I was washing my 1960 yesterday and notice that water tends to pool up in the rear of the deck due to the fact that the drains are slightly raised off the deck. Even with the covers on the scuppers open, it still takes a while for all the water to drain since less than half the drain hose diameter is aligned with the deck surface. I'm sure there's a good engineering reason for this, so I'm curious as to what it is.