I certainly don't want to start a pissing match but I beg to differ with you on this statement.
First...NOTHING is free...You are correct by suggesting a builder could just polish the pins on their own time and use their own electricity and use their own polishing compound and use the wear and tear on their own machines.
But it's certainly not free unless you've stolen it.
Secondly....if you do any research on the subject you will find out it is almost impossible to duplicate the electro polishing technique doing the individual pieces by hand.
The added cost is minimal to the added benefit you'll receive. Yes, you have to send a large lot in at one time for it to be cost effective. But some manufacturers of products would rather cut costs and present a lesser quality of a product at a reduced price of their competitors....
and that's fine also.
Thirdly........No, I do not buy pins from the individual promoting the electro polished product.