All oils are not created equal, just because it is synthetic doesn’t mean it’s a good oil, also some cases, a semi synthetic or mineral oil can outlive a synthetic with the right additives. I am a reliability consultant in the lube industry, specifically high quality oils and greases along with lube systems. A good quality oil can easily run 10k and I have seen testing on over the road rigs in Alaska, about the worst conditions a truck can see, going over 60k between oil changes on specific quality oils with a good additive package, while doing filter changes every 10k. I personally go over 10k on my car and truck with no hesitation with the oil I am using.
Newer vehicles with engine clearance needs or high temp/low temp issues would be the only reason in my mind to go with a full synthetic. Synthetics don’t carry additives as well as mineral oils. Yes, the oil doesn’t break down as fast as a mineral but the additives are really what do all the wear protection. If it isn’t calling for a full syn in something like a 0w-20, 5w-20 or 5w-30 I would suggest going with a quality semi synthetic with a good additive package. If it calls for a 10w30 or 15w-40 I would only suggest a semi syn or a mineral oil with a robust additive package.
Edit: I should also add, full synthetics are not bad, I should have said the right syn with the right additive package if they are calling for a full syn, which most newer vehicles are. A cheap full syn from tractor supply might only get you 5k, a good syn oil with a good additive package can easily go over 10k. Just research that it is a good additive package in any oil you plan to run it ver 10k or better yet, get an oil test done with the oil you are using at 10k and see how it is holding up. Test will cost you about $30 and you might find you can go 15k or 20k and get a baseline. Might save yourself hundreds in oil thru a year.