Parts sales and hobbyists cannot sustain a chain of stores this large with this much overhead. Rent alone on the storefronts is a huge OPEX.
It's all nice to have dreams of the 1970s when hoards of people came in to buy tubes, transistors, shortwave radios and stuff we like as hobbyists, but those days are long over.
Consumer electronics have shifted to disposable items. It broke? Go to Gabrage Mart and buy a new one. Not even the big name manufacturers provide much parts and service support to professional service shops anymore. Nobody outside of hobbyists and engineers even try to repair electronics. Nobody. E-waste is a huge problem because of this.
RadioShack rode the cellphone wave to keep the company afloat, borrowing from Peter to pay Paul. For every profitable location in a given district, there are 10-15 that have been chronically losing revenue for 20 years. The cell market is saturated and you can get a phone at Kroger of all places. And for less than RS.
Using your four function calculator, the numbers just don't add up.
There just isn't money in it anymore, and hasn't been for quite sometime.