Atheists believe that man created the gods he worships.
Most of what we term "prayer" issues from desperation.
A farmer would plan for a fruitful harvest, and suddenly a drought would begin.
All his efforts would have been useless, and he'd have no say in it.

Of course, he would understand that matters were beyond his control, and above his muscles.
But would he understand that it was simply nature being nature?
He would assume a god somewhere was angry with him.
Maybe it was because he killed that mother deer last week.

Or because he destroyed an anthill the other day.
But he needed to beg the god of droughts to leave him, or the goddess of the rains to have mercy on his poor, ignorant soul.
And so, the sacrifices would begin.
A goat here, a cow there; a human if the drought lasts too long.

Prayers issue from a place of helplessness, where you understand that without a "divine" push, or a stroke of fortune, you can't get much done.
The present issue is that people expect God to take care of them, simply because He said He would.

Many of them don't till the soil first, plant seeds and water them, before praying if a drought ensues.
They sit at home all day and go straight to prayer.
Then when—without work done—nothing happens, they go:
"God! Where are you?!"