There are a lot of rip-offs in this world, auto repair isn't their only business, lol.
As a business owner for many years, not auto repair

, there are some things that make my costs higher than just the labor.
Since I warranty the parts I install I get the most reliable parts, not necessarily the most expensive but almost always not the cheapest.
And since I don't make the parts myself I have to rely on the OEM to make a quality part that won't fail.....................well I have noticed that the quality control even on the better parts are not what they used to be, I do notice more failures in the last 10 years, not a lot more but not a 0 increase.
So to stay in business(make money not lose money) I have to spread that cost of a redo to the cost of that part, i.e. how many do I install each year and how many fail, and what does the failure cost my business.
Yes the OEM, in most cases, replaces the part free to me but I still have the labor cost to replace it.
How is that your problem??
If you expect a warranty then the business must still be around when you have a problem, so........if they are not making enough to cover warranty repairs then they won't be in business.
I do install customer supplied parts, but with no warranty on any thing, years ago I did warranty on the labor, but not any more, too many hassles with customers, and OEM, about who is at fault, every one wants someone else to pay, lol, so now it's no warranty, so no misunderstandings.
A few auto shops will install customer supplied parts with no warranty at a cheaper price, that is always an option.