If you have no desire for one, don't buy one. Beats me what you are looking for here, short of trolling against certain guns. If you feel you have to justify each purchase to include a gun, my sympathies, your life must be boring.
Many who purchase weapons like you mention do it just because they want to. They buy them because they admire the weapon, it's design, or just flat out enjoy shooting it. AR's are very accurate, and can be made to be extremely accurate. Many, many shooters compete in marksmanship contests with them. Some like to shoot them for the pure fun, including plinking. (I love plinking, with .22 or any other rifle or handgun) I also target shoot, challenging myself to improve.
AR's can be used for hunting, and in fact are used by many hunters for that. Coyotes, feral pigs, etc are well taken with an AR. AR's are easy to shoot, with the semi-auto action and straight stock design delivering a very reduced recoil.
Personally I have no use or desire for an AK. I don't feel they are well made, accurate or of any use for me. So I don't have one, do not plan to ever buy one. But, I know there are many who enjoy the weapon, good for them, have fun. Just not for me.
I didn't need to ask anyone why I should or should not buy one.