Why do people want you to do stuff thats out of your job description?

Every job description contains, expressed or implied, "and additional duties as assigned". A job description contains the major duties. Sure you can refuse, and will most likely be fired. If you are under a contract, the answer might be different.

Most job descriptions include "and other duties as assigned". A job description is not a contract. You risk being considered not a team player if you refuse to do other things you are asked to do. If your supervisor is asking you to do something, do it. If a co-worker is asking you to do something that's really their job and not yours, you can politely decline, saying you are busy with your own tasks, but be careful. You may need help sometime.

You can refuse; this is insubordination and you can be discharged for it. Job descriptions are general guidelines and any respectable and accurate HR person who approves a job description will make sure it has a "catch all" phrase that says something like "other duties as supervision and management directs" because it is not possible to write a job description that covers everything and because the business world and therefore the job world is dynamic and changing all the time; if you fail to change with the need you and your business dies - and no one has a job. Do your job as directed by supervision. Keep in mind that the more skills you develop, the more you adapt, the more willing you are to adapt and take on more jobs the more valuable you are and the less likely you are to be discharged should the economic activity slow down (and economic activity will rise and fall). If you want to be a long term worker - adapt, cooperate, adjust, and stop the reluctance to learn new things. If you refuse to adapt you better adapt to a new employer. This question reflects immaturity of the employee more than anything else.

Something to consider is that people who insist on sticking to a predefined list of duties are the ones who stay put in one position their whole careers, never moving forward. The ones who go above and beyond the call of duty are the ones who move up the ladder, so to speak. You still get paid the same whether you are doing ABC or XYX.

As a manager, I have no room on my team for people who are inflexible. Now, I don't make them do MORE work, but we do have to do DIFFERENT work, and quite often at that.

You have the right to refuse to do tasks outside your job description and your employer has the right to immediately fire you. Basically, in the U.S., a job description is not carved in stone and your supervisor has an almost unlimited right to assign your tasks which are not spelled out in the job description. The only jobs you cannot be assigned are those which may require a certain level of education, a license, or a certification. For example, an orderly at a hospital is not going to be assigned to perform a surgery but can be assigned to housekeeping duties.

Need more to go on. While you shouldn’t let yourself get taken advantage of, people with more capabilities get more hours. So let say I just wanna serve tables, but they ask me to do other things like cook or do dishes. I have a right to tell them no. But then I’m only gonna get a servers hours. Back when I had sh*tty jobs like that, I was the man. I did everything, cook, serve, dish, bus, host. And my hours showed that, made more money than everyone except the GM. Still wasn’t making enough money, so I quit that bullsh*t. Now I am a flooring contractor. But still, if they ask me to do stuff out of my job description like move furniture or do plumbing and whatnot, I’m not gonna tell them no. They will see that extra expense in the invoice. So yeah, I think you should do more, just make sure you’re getting paid for it. If they try to low ball you then you tell them to go f*ck themselves, well the nice version of that anyway.