Why didn't hippopotamus power take off like horse power did?

One time horses were a common site pulling carriages, ploughs, long boats etc. Although mostly replaced by machinery these days they still have a role to play and are a familiar site in the country.
Not so much for the hippopotamus. So why did hippo power fail to take off like horse power did? With rising gas prices and green issues being a concern is it time to give the hippopotamus another go?
Why didnt hippopotamus power take off like horse power did?
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+1 y
Ok hippos are slightly dangerous, but thousands are killed in cars every year. There's never once been a massive hippo motorway pile up.
Why didn't hippopotamus power take off like horse power did?
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