Why do abusive caregivers think doctors believe obvious injury lies?

It's very offensive when a small child or infant gets injured so badly and they lie about how they accidentally fell or rolled off the bed.

When my son was 7 months old, he rolled off the bed and hit the hardwood flooring (I saw it happened right at the time I came back into the room and was far from reach; even if I had dived or thrown myself, I still wouldn't be able to catch him) while under my husband's care and we took him to the ER immediately. Nothing happened and he's now a very active, smiling 13 month-old boy. But it's very offensive when some pathetic child abuser thinks hospital staff will fall for the ''he/she rolled out of the bed, fell on the floor, etc'' or other nonsense to explain all the injuries and fractures found... which doesn't coincide with a common fall or accident. Secondly, in those cases there is a huge lapse of time and the reaction isn't is different. Even if was a genuine accident, the caregiver would be very emotionally and taking the child to the ER right away.

Then they get caught in the lie and that's when many finally admit what they did. Honestly why do they think they can get away with lying about it?

Updates
6 d
Then the poor child either has permanent brain damage or dies... and they still think hospital will believe the obvious lie. Why?
Why do abusive caregivers think doctors believe obvious injury lies?
Post Opinion