It isn't that we need to decide exactly who contributed proportionally and how much of the profits we get. We're really just reaching for something that increases wages faster than raises.
And really it highlights the issue that not only is it hard to get fair profit-sharing, it's also hard to get market-competitive raises.
But of course a company is going to say it's hard to decide who gets how much, because they have an incentive to pay their employees as little as possible, regardless if it's through base wages, raises, or profit sharing. There always seems to be an excuse.