There also is a lot more to document. That Marantz receiver or shortwave radio probably had less than 100 transistors. Your smartphone has billions. The cost of providing documentation alone may be sufficient reason not to provide it to customers (yes, they have documentation, but that may not be sufficiently checked for use in a B2C setting, where you likely can’t provide documentation with a “reality may be different” disclaimer)

I also think that, historically, electronics were documented because they broke down so often.

You just had to be able to spot a broken tube in your radio, clean a potentiometer, etc.