I agree that you can "just renounce" although notice that this won't necessarily work (it will for the US assuming you follow the procedure properly)

However being a dual citizen isn't necessarily all upside. Citizenship comes with requirements, particularly in some countries military service is mandatory and so if you're a citizen - even though you are a permanent resident of somewhere else, you must either go do your service or maybe pay a fine depending on the country.

You also get treated differently if things go wrong. Foreigners are entitled in most cases to diplomatic assistance from the representatives of their country. Your country can't necessarily do much for you, but typically you will get that phone call home to let loved ones know what happened, they can find a lawyer who speaks your language (but you'll need to find a way to pay them), if there's some paperwork snafu they might be able to help (often for a fee). It's at least nice, if you're jailed or in hospital after surprise food poisoning or whatever, to hear somebody who speaks your language.

None of this applies to dual citizens. You're "home" from their point of view, so no need to contact your diplomatic representative, maybe you have never been there since the day you were born and can't speak a word of the language but too bad.