If I owned a tire shop, I too would perform tire patches for customers. My reason would be that a customer wants to feel they are getting their money worth. However, when I have a truck that needs to be on the road in 5 minutes, and an internal tire patch will take a MINIMUM of 90 minutes longer than a plug, (drive time, waiting in line... ) there is no real choice. If plugs had a 50% success rate, I would be dubious. However, they have a 100% success rate with me over the last 26 years.
Since I am in the poop business, I deal with plumbing issues as well. If a customer has a plugged toilet, and I plunge the toilet and charge them $95, they will freak out!! If I plunge the toilet, (solving the issue) then remove the toilet, run an auger through the toilet, rod the pipe from the toilet to the septic tank, run a video camera through the toilet and main pipe I just "cleaned", and charge them $400, they feel much better. In my own house, I will just plunge the toilet, because I just know better. (by the way, I ALWAYS give the customer the choice, and they ALWAYS choose the more thorough, although more expensive route)
Same as installing a patch vs a plug. Same result, less time and $$$. More convenient. But I wouldn't do it for a customer if I was in that business.
Also, a tire patch isn't $20 as stated earlier, it's more like $90. Possibly a car tire, but not a big truck tire. I just had one done when I was out of town. There are mount/dismount charges, shop supply charges, possibly even a tax or two if I remember correctly. And that was on an outside tire! Now, add driver time, (on overtime) fuel to get to the tire shop, and you can easily exceed $150-$200.
Customers that are expecting you to be on time get upset, and may not use you when they need service again. It happens, trust me. In a customer's mind, there is NO excuse for a company to be late. I've been on the receiving end of those phone calls, and it's not pretty!!!
Plugging will continue to be my first choice.