Sharks don't eat people, they bite and then realise they're not very tasty.
It is true that body parts have been found inside sharks but they weren't meant to be there.
Thank you David Attenborough.
There isnt enough fat on your typical human, we simply are not nutritious enough to be worth eating.
Filling up on Human would be like filling up of polystyrene and then finding that you cant actually eat any more when a decent meal comes along.
Thats why the sharks will usually spit us out.
Back in the 50's my Mum had a friend who was bitten by a shark while swimming near cape town. She was uninjured despite being grabbed round the middle. The conclusion was that the one piece woollen swimsuit that she was wearing at the time was not to the sharks taste. Lucky Woman!