Kakashi isnt shinobi enough to kill obito
kakashi was an arrogant bastard until obito changed him. Obitio is the reason kakakshi is who he is today, Kakashi did not care about comrades he cared about completing the mission
and rules that a ninja must follow. Obitio changed that wen he mentioned he respects the white fang. Kakashi then started to care about comrades but obitio would die and give up his eye
He vowed to protect his comrads after that.
Kakashi's personality changed and he picked up a lot of obitio's noticable traits. He is always late when showing up to his students and comes up with excuses just like obito did
and he taught his students the value of their comrads "those in the ninja world who break rules and regulations are called trash but those who dont care about there comrades are even worse than trash"
Because of living his life like this kakashi will feel like he cant kill obito he thinks obito is still deep down there somwhere
and he doesnt want to see another conrad die so i think he will just let obito kill him