Currently, there's a huge amount of people doing shit jobs. If all these people would earn enough that they would want to do these jobs even if they had other opportunities, (a) the money would have to come from somewhere and (b) a lot of people would earn a lot more money all of a sudden.

Those people earning more are also the people buying stuff, so stuff would instantly get more expensive.

It really doesn't matter whether you are doing it in a sudden jump or gradually, the prices would track the wages.

Let's take a super simple example and ignore the economical bigger picture for a second. Let's take the example of a strawberry picker.

In my country, a strawberry picker earns about €2300 per month. During covid foreign strawberry pickers couldn't get into the country, so the farmers tried getting locals. Thanks to covid unemployment was high, so theoretically there was enough free labour. But nobody wanted to do the job. They even increased the pay to ~€3000 per month and still nobody wanted to do it.

Most strawberry pickers in my country are from Rumania, a country where the median income is about 1/4 of what it is in my country. So as a rough estimate, so that the wages are worth the same for locals as they are compared to Rumanian cost of living and incomes, a local strawberry picker would have to earn €9200. With that income I'd also be tempted to do the job.

But not only the strawberry pickers, but all the people working crap jobs in the supply line would require a similar wage rise.

That means, for the strawberries to still be worth the cost of labour, their price would have to increase similarly. And now our fictional strawberry picker can afford the same amount of strawberries with their new €9200 wage that they could afford before with their €2300 income.

Do the same thing for all shit jobs and the prices of almost everything will have to increase the same way.

So if they wanted to eat, they would still have to work, and most likely they'd have to work the same shit jobs.

I am not arguing that this is a natural law in any way. As you said, economy is not a natural law. But if we keep our economical system the same and just change that one thing without adjusting how the rest of the system works, the maths of our current system will balance it at the same point.

To pick up your example: the abolition of slavery needed quite a few changes in quite a few places. Namely, former slaves got the status of citizen and that gave them a ton of rights.

If the abolitionists had changed nothing except making the state of being a slave illegal but didn't confer any new rights (e.g. right to choose a place of employment, worker's rights, right to freedom of movement, right to own property and so on) to these former slaves, then it's quite likely that a lot of former slaves would find themselves in a very slave-like state because they have no other choice.

If you want to change a system, you need to change every single mechanic that touches the things you want to change. It's hardly ever enough to change one value and call it a day.