> Buy a few million of them from a manufacturer, and you will find the 5% ones still significantly cheaper

That just ain't true. 5% are not really used (at least with consumer electronics). 1% and 5% difference is very tiny, even across few millions.

> That's why new 5% and 10% resistor products are still sold.

If you go on digikey and search for 10% you will not find very many compared to 1%