That's all well and good when you're working in a big mindless factory, and your hired to churn out widgets on a quota system. The problem is, often enough I'm looking to hire someone with a little more brains. I want someone who's going to bring some ideas to the table, who's going to think outside the box. I want them to speak up, and there isn't anything like, "I'm going to steal your ideas and present them as my own, and take credit." It's not a big mindless factory that would allow it. If you can come up with a way to save the business money, you're probably going to get a bonus and/or promotion at some time soon, because you're doing good work.
Now arguably a situation like that is a rarity, but part of the problem is, even when you're in that situation, it can be hard to find good people to work that way. It can be hard enough to find people who will do a job when you set out simple instructions to follow. It's much harder to find someone who has enough judgement to know when to follow the instructions, and when not to. When you can find someone like that, it's worth something extra.
Now I understand the desire to get a good job with nice, clear-cut responsibilities-- churn out 500 widgets, and if you do that, you get paid, and it's all that simple. Not all jobs are like that. Especially working for smaller companies, sometimes it boils down to, "I'm just trying to make my company successful. If you can just get done what I need to get done, I'll keep you around. But if you can help me figure out how to improve things, then I'll be trying to figure out how to keep you happy, because that's hard to find."