These jobs should be rewarded more, but lower-skill jobs should still provide for a decent life, which they don't. Having to work two jobs is a failure of the system, not the individual.

Having worked in both low end and high end job I have two answers to that. The first is social status. No matter how much you earn, you will always be seen as more intelligent and more "worthy" because you have a higher status job. I think for a lot of people it's this admiration that would be enough. The second answer is physical reasons. My sister's back has been shit since she was 30 because of her endless standing in a barista job. Some jobs are insanely hard and just the comfort of being able to take a coffee break and a chat and sit at your desk is absolutely worth striving for. (There are people who enjoy manual and physical labor, but then again, why punish them financially, if they are willing to do the "harder" jobs?)

And yes, a third answer would be the urge to learn more and be more.engaged mentally. But wanting to do that and that having to do that to achieve success are two very different prerequisites.

why would anyone work hard to become an attorney

Do you really think becoming an attorney is harder than, say, cleaning toilets 40h/week? I finished my master‘s degree in physics recently. Has it been stressful? Sure. But I could mostly choose my own rhythm to work, had a healthy balance of exercise and leisure, and had coffee breaks all the time. I know a carpenter and some farm workers, and I would have chosen uni over their work at any time. And chances are, once I get a „real job“ it will still be less hard than working on a field.

Wages are mostly a measure for how replaceable you are, not for how hard the work is.

It's fine to reward those who've spent more time and effort more - as long as we remember and acknowledge that we need everybody else to make society work too, and the baseline of even the lowliest workers is reasonably comfortable.