OBITO GAVE UP that's Why
And Chose To Follow Madara Foot Step Because The Dream World Seem So TRUE TO HIM
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If anything, he did'nt give up.
In fact, his sole reason for tsuki no me is for him to be with Rin again in the way he sees fit.
I could guarantee you that seeing your ''best friend'' who you actually sacrificed yourself for killing the oove of your life would be quite devastating.
Although I'm sure there's a reason for it, Tobi sure as hell does'nt know it, and why would he even expect a good reason for it anyways?
All humans are per definition evil anyway.