>>91110470>Autistic answer ahead:Jack would eventually come across Aku's primordial form as a non-sentient, reactionary lake of black goo and he'd delete him from existence right then and there. I doubt he'd even manage to gain enough sentience to adequately combat him while Jack's destroying his said black life essence in the process.
Sending him back to the time where he had just gained his sentience (thanks to the poison arrow from Jack's father) wouldn't work either, because he'd have to deal with TWO extremely skilled samurai wielding TWO magical katanas. Not to mention, they're father and son, so they'd have an innate desire to protect each other while being far more synchronized and team-oriented with their combat skills. It's a double-whammy.
So it was actually smarter for Aku to throw Jack into the distant future. Aku was able to expand his rule onto other planets and galaxies, and in turn gather millions of forces, assassins, armies, demons, droids, monsters, bounty hunters and so on to hunt him down. So Jack has far more to worry about than just Aku. Not only that, but Jack loses his family, his people, and his cultures from the old world in the process - forcing him to start out with nothing.
Rather, the better questions to ask are:
>Why didn't Aku just fling the sword into the distant future or the distant past? If he had separated the sword from Jack, then Jack wouldn't have a chance of defeating him and it'd be game over right then and there for the first episode.>Why has Aku only flung Jack into a time portal once? Why not just keep throwing Jack further and further into the future whenever he confronts him? Could he only use his time portal ability once, and if so, why? Are his eldritch reality-warping powers severely limited or unstable? 
