It's a major reason. Back when TVs were made of tubes, you could expect any tech-savvy guy to be able to learn how to go in there and swap the tubes out.
Nowadays? A techpriest that can take apart Apple's iPhone stacked PCB assemblies, replace large BGA components in there, and then put them back together and have it work is a rare specimen. And "rare" means "expensive".
A hour of labor of someone who does neurosurgery on electronics isn't going to be cheap.
Not that Apple has any good reasons to make it even harder on the madmen who attempt and learn such repairs.
why are Apple (Foxconn) assembly workers paid so little?
Because they put assembly in countries with cheap labor, and optimize the assembly process so that most workers don't have to perform any complex operations, or any operations that involve thinking.
Things like PCB manufacturing? Putting those BGA chips where they go? Done entirely by machines.
Now, a notable exception to this rule is the "rework" or "remanufacturing" lines - where actual human specialists take devices that failed QC, or used devices, diagnose them, and bring them up to standard.
Those can be very involved. But official manufacturing still has strict limits on how far are they willing to go - and unofficial refurbishment lines have them beat on repair complexity.