It can (and always does, in practice). I worked at a company that restructured it's wage and salary schedule. Our base salary was reduced by 20% and we were "gifted" with a generous profit sharing plan. The first year, the owner's wife blew all company profits on a vanity project - zero profits.
You'd likely get a pay raise if the profit sharing plan were canceled (assuming you generate profits).
All profit sharing amounts to is employers pushing risk onto their employees. If the employer ****'s up and doesn't make any profits, they get a break because they won't have to pay employees as much.
The bottom line is - I don't want to accept risk for decisions I'm not making.