Well there are multiple reasons for this so lets break down the main ones which are costs, quality and process. All of these factors will determine if you are getting a good value.

COST - This will include everything from the cost of the person performing the service to the cost of the parts used.

1. Labor - Not all employees cost the same. A young technician in training will cost much less than an experienced seasoned technician. Where this can matter for your basic oil change is important. An inexperienced technician is more likely to make a mistake that can become a major issue down the road. If your oil change comes with an inspection, as most of them do, an experienced technician will be much more knowledgeable on what to look for in order to keep your car safe on the road.
2. Parts - Low quality oil is very cheap compared to a high quality oil with a high rating. The same is true for the filter. A cheap filter does not effectively remove contaminants like a good quality one. Good quality oil and filter can cost as much as three times the cheap option so you really need to know what you are paying for.

QUALITY - The quality of the labor you receive and the parts that are installed can make all the difference.

1. Labor -  What training and experience does the person changing the oil on your car have? This can be the difference between a stripped drain plug requiring a new pan to be installed and a properly installed and one torqued to the proper specification.
2. Parts - Not all parts are created equal. There is a very big difference between a highly rated high quality oil and some of the basic low rated oils on the market. The same is true for the filter. Filters have different qualities inside and one will do a much better job then the next. This can have a big impact long term to your engine since these parts are there to protect your engine. That's why you are getting them replaced!

PROCESS/VALUE - What is getting done during your oil change?

1. Most shops will be replacing your oil and your filter with new but ask. Some places actually only replace the oil and the filter is extra.
2. Check and top off fluids. This is common practice but its worth asking if they checked and topped off if found low. 9 out of 10 cars will take some washer fluid and that is not free so find out if that is part of the service.
3. Inspection? Some shops will perform an inspection but some do not. There might be a very big range on what is all looked at. This can be anything from a verbal “we looked at your tires and brakes” to “we performed a full digital inspection of the vehicle with pictures and videos”. The idea behind these inspections is to keep the car safely and reliably on the road for a long time so a good thorough inspection is a much better value. 
4. Reset your maintenance indicator. That pesky light or message on the dash. Not all shops have the knowledge or tools to properly reset these very helpful reminder systems.
5. What else do they offer? 
6. Can they perform a good inspection? 
7. If things are found can they take care of them for you? 
8. Do they offer a ride to work?
9. Or a loaner car during repairs? 
10. How about a car wash? 

All of these things add “value” so understand what you are paying for. 

Remember, the reason you change the oil in the first place is to take care of the engine so it will last for years to come. Consider the “value” you are receiving. Just putting some oil in the car is not good enough. Make sure its high quality and done professionally.

Keep the rubber side down!