From my perspective, containers have a bottom that breaks the continuity to the ground underneath, but in a raised bed the soil is a continuous column. That is why you must use very loose, fast draining soil in a container (think potting soil). You can put really dense, clay-rich soils (whatever you dig up from between the beds, usually) into a raised bed and the drainage will still be quite good.
The key here is a continuous column of soil to provide capillary action that moves water up and down in the soil. My college professor used a sponge to demonstrate this. Saturate a regular sponge while laying flat. It holds a lot of water. Now stand it on end and what happens? A lot of water drains out of that same sponge because the sponge is "deeper" when the held vertically. Now, when it stops dripping, touch your finger lightly on the bottom and more water will run down your finger because adding your finger suddenly "deepened" the sponge. A deep column of soil, even of poor quality, acts like the sponge on it's end, pulling water down from the top and increasing the drainage. Of course, capillary action will also bring water up as the top dries. It's self-regulating within a wide range of rainfall/watering.
That is the "magic" of raised beds, rock gardens, etc. It's far easier to get the amount of water right than it is in a container.
we can always count you to give us the true explanation! thank you for this.
I was thinking it was primarily related to drainage....................but otherwise I augment the soil and keep both systems light an airy soooooooooooo then I was just thinking why build a raised bed?
maybe a bottomless container might be similar to a raised bed? for the capillary action? not sure but I know who knows..................