You don't mind but some of us prefer to have functioning tools and access to spare parts without a lot of hassle. Proprietary parts does not make life easy.
As OST mentioned it's not hard to source a KAC bolt.
If you want to have spare parts then order the bolt from OST just as you'd order a spare for any other AR-15. It really isn't as difficult as we're making it out to be...
Now if we're talking SHTF/End of the world type scenario then remember you can drop a regular bolt into the SR-15 and it will work in a pinch.
no one has addressed my other point about not seeing any performance gains in the KAC over the DD, because there aren't any that are worth the extra cost.
A few things that pop into my mind are ambi controls, included BUIS that are arguably the best available on the market, softer and smoother recoil due to the intermediate gas system.
Let's also not forget to mention the E3 bolt as we all seem very concerned with bolts breaking. There hasn't been a reported E3 bolt break with standard use as far as I'm aware... The same cannot be said for a regular AR-15 bolt.