Technology

If the expectation is outlined at the beginning as the job monopolizing my time and me doing whatever work comes along when I’m on the clock, then that’s the job I took and I need to be available to them.

Yes. THAT is the expectation we are talking about. If a company doesn't expect that, then there is no issue.

in a lot of jobs the expectation is just to meet certain targets of work to be completed. If I meet those targets, the employer owes me the agreed upon wage.

Great. If that's what your employment agreement says there isn't a problem. Congrats on finding a white collar salaried job that involves no collaboration or expectations on availability.

If I pay the grocery store a dollar for an apple, am I entitled to as many apples as they can possibly deliver me? Obviously not.

That's akin to hourly pay. You work an hour you get $10. You buy an Apple you pay $1. Salary is like an all you can eat buffet. You pay $20 you eat 1 Apple, 2 Apples, 3 Apples, etc. But also there are rules; Can't take anything home, can't share your food with a non-paying person, you'll probably get cut off at some point if you eat too much or waste food etc.

If I pay a worker a dollar for a task, am I entitled to as many tasks as they can possibly deliver me?

I think this is the big misconception. You're describing contract work, not salaried employment.