Maybe he can't because traveling back in time means he can't use his plundered abilities. In the new timeline, he didn't aquire them "yet", which would of course mean that he'll lose his time travel ability the moment he uses it.When would this end though? If Yuu obtains time-travelling powers and he gets horny with Tomori, he's pretty much obliged to save her brother as well.
And without powers, I don't see a middle-school kid (I'm guessing he'll switch into his old self with a "new mind", see: butterfly effect) achieving it just like that, which is why I wonder how his brother made things possible in the new timeline, as a kid. Probably won the jackpot a few times.