Where exactly did you see bicycle riders that ride like that? In an organized race?

Riding "in the drops" will indeed reduce wind resistance, but in everyday street riding cyclists don't ride like that permanently. Continuous riding "in the drops" is something you might see in an organized race, but when the very same cyclists ride on the streets they usually ride "on the hoods". This is by far the most popular riding position for bicycles equipped with drop bars. Outside of a race the "in the drops" position is usually used only temporarily, when riding at maximum speed downhill. Once at the bottom of the hill, cyclists usually exit the drops and switch back to "on the hoods" position.

The "on the hoods" position is more upright than "in the drops". If you so desire, you can also ride in "middle of the bar" position, which is even more upright. But I personally find the "on the hood" position the most comfortable.