That's how EVs started! Sorta.
This is from a Porsche in 1900:
And some 2000s EVs tried it. But it's impractical.
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It increases unsprung weight, e.g. weight not cushioned by suspension. Bad for ride/handling/steering feel.
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All that vibration is HARD on the motor. Read: unreliable.
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Motor is more exposed to temperature/dust. Again, reliability.
In reality, a decent suspension needs a lot of room under the body anyway. An axle to get the motor in the body is dirt cheap on the rear, and still pretty cheap on the front, and you could just mount this thing sideways to make it flat...