The problem you are missing here is that it creates a loop. I’m going to ignore the idea that people will do terrible jobs for lots of extra pay, because there are many jobs that people will not do if they can avoid it without an extravagant amount of pay, far beyond what is possible, but I will brush that aside to start with.
We can start with the simple case of McDonald’s. The working conditions are not great, and you flip burgers. UBI starts, and people demand more people or they leave, because it’s not worth their time. You have multiple things happening — one, more people start working part time to an extreme, as a contractor-styled economy, and two, the prices at McDonald’s will have to rise to compensate.
Now that McDonald’s prices are rising — the same thing would happen across the board. Now all these crap annoying jobs have to raise their payment rates, and thus raise their prices. Now suddenly, commodities like bread have doubled in price.
What happens to the UBI? It was enough to cover rent and food, but now it isn’t. Do you increase the UBI?
The loop starts, and doesn’t end, because UBI is trying to create value from nothing.
The only way out is full automation, and we cannot have a UBI until automation is truly in our society. Automating fast food cashiering is not automating our society, because we have so many critical jobs that cannot be automated — even simple ones such as plumbing, construction, electrical work, remodeling, miscellaneous things like that.
As we progress in society, UBI is a valid thought process for later — but not now. It is only a thought process to be considered when we have excess automation to handle all of society, and we can let a significant portion of the population do essentially nothing.