Oil change frequency

Why does Kia recommend changing oil every 7500 miles or 6months when Synthetic oil is good for 10k miles. Or atleast that is what dealers and car companies promoted the high price for synthetic oil and charged double the price.

I drive my car everyday and most of the time one way I drive 3miles minimum. I drove little less than 3k miles in 6 months.

My question is do I have to follow this recommendation? Or can I drive for a year and change? The oil change costs $99 where I live.

No, I cannot and do not want to change myself.