Answer:
Step-by-step explanation:
I would imagine its because his theory changed just the very basis of what was accepted as truth at the time. Just like if someone told you today that the Earth is actually shaped like a triangle (it isn't-I'm just saying that to demonstrate how absurd it sounded).
In their minds it was very hard to grasp how the Earth was constantly orbiting the Sun, since so much in their everyday lives seemed to oppose the idea. If the Earth was in constant motion, why don't we feel it? Now we know and can prove that it's because Earth moves at a constant speed with us. We don't feel it, because we're moving at the same speed, kind of like how we don't feel like we're moving all that fast while inside a moving car.
Anyways, at the time, I believe that the concept was overall just hard to accept when everything pointed against it. This is just what I've gathered with my limited knowledge though, so take what I say with a grain of salt!