because exynos is samsungs processor and they want to implement it as they could do better optimization... in US exynos implementation has some copyright and legal issues so they are not using it in US phones.... if they could they would make all the...
S8 is phone with gr8 hardware but falls in the same category of samsungs bad software integration. Samsung Experience could be faster at time but could get sluggish at times, battery is good, display is great, micro SD hybrid slot is a much needed o...
I seriously think Samsung are the best in making hardwares but on the softwares front they lack a lot... I have also updated to Oreo on my s8 I don't find any improvements in the performance of the device...the main culprit is the Samsung experience ...