[scheff]

2 reasons I can think of.

1 - nobody would get a pay rise because "If I give you a pay rise, then I have to give everyone a pay rise" would be the mantra of managers in an established organisation. Anything less would create arguments.

2 - the ego of every employee. "Oh, right, just because he's an engineer, he's more important than me in marketing ... which one of us improves how much profit you generate?" ... and so for every other class of employee. even between engineers - "I'm sorry, but I'm better than that guy because of X, Y and Z (subjective reasons) and I should get paid more."

The extension of 2 is - "If I don't get paid the same as that guy then I'm not working nearly as hard as I have been ... I mean - what's the point?"