Exactly - $$$$$

The money it costs the airlines to pay for injuries to passengers and crew. Injuries from passenger bags is one of the most common forms of injury to passengers (where I work anyway). I can't remember where it placed last year but it was in the top 3.

Where I work assisting with hand luggage is at the discretion of the crew member, and if they do help there are certain techniques that should be followed, like using a 2nd person. My rule, if you can't lift it - neither can I (Of course with a few exceptions - I'd never expect my grandma to reach a locker but if her bag is too heavy I'd still gate check it!)