To the bolded, because of two reasons
1) I have integrity and don't like to gouge people
2) While I could certainly make money fixing screens, that isn't the majority of their business. Which is data retrieval + wipe + reinstall. Also sales of accessories. Used to work at firedog, geeksquad, and even compusa repairs. I know how to fix computers, but everything about phones which I would have to learn.
When I speak of oil changes being about as easy skill wise as replacing a glass screen, this isn't me talking out my ass here. I am very mechanically inclined, but just don't always have the time. I helped build cars, rebuild engines, build computers, put together laptops, and build my own devices. I've repaired most of the major appliances in my house including fridge, washer, dryer, lawnmower, and dishwasher. I've worked on small things as well as big things. When looking at screen replacement the only "tricky" part to replacing most of them is making sure not to break the digitizer and that is it. Everything else is just heating up adhesives, prying open the pry points, and unscrewing a few screws. Which is exactly what I plan to do when the replacement parts come in for my wife's phone.
Again, I would normally have no problem tossing $50-$70 for someone else to do it to save me time. I just have a hard time paying price gouging prices.