Because realistically it's not really half as much. It's less than $50 for a full synthetic oil change at Wally World, but after I buy the filter and oil, what did I save? It's 23 for the oil, $8 for the filter for a total of $31. I've saved $19, which is a reasonable amount. However I buy the same oil and filter, take it to the local tire store, and they do it for $10-15 depending on who rings it up. Either way I am not complaining. At that point it's not worth it for me to get out the ramps. I drop it off at night, pick it up the next day, and here's your $15. Some things are worth doing yourself, oil changes aren't one of them in my book.
I think there are a lot of factors that can play into whether or not you change your own oil. That $19 savings is likely a much bigger deal to someone like myself who brings home $25k a year than it would be to a guy who makes much more.
The type of vehicle you drive is also a factor. In your case, you have to pull out ramps to get the job done. Ramps you had to invest in of course. I drive an SUV that I barely even have to crawl under. No skid plates to take off or anything. Just halfa** lay down in front of the bumper and remove the plug. Filter is right there easily within reach as well.
The biggest reason I do it myself though is all the people I know that have been screwed by these places. My grandfather drove a Dodge Dakota with the 3.9 V6. Took it to Kwik Car for an oil change. They put in the oil amount for the 5.9 V8, Bad things happen when you put in an extra 1.5 quarts of oil
I was out of town working for most of last year so my girlfriend had to take her Monte Carlo to the Chevy dealer to have her oil changed. When I got back and her car was ready for me to do the next oil change, I noticed the oil filter was never changed at the dealer. I knew this because I write the mileage on her filters with a sharpie.
I could go on with several similar stories but I'd likely develop carpal tunnel trying to type it all out.
One thing I can definitely see is the guys who wrench for a living not wanting to change their own oil. I'm a plumber with a kitchen faucet that could use a rebuild. Probably not gonna happen any time soon.
I do work with my hands all week but not on cars so for me, it is still kind of a hobby even just doing a simple oil change or brake pad replacement. I enjoy my alone time on Saturday mornings doing these things along with checking tire pressure and adding if needed. I'm kind of a spaz about proper tire pressure so this gets done every weekend.
Anyway, sorry for the novel. Just a few thoughts I had and wanted to share.