Honestly thinking about Uka and Cortex more I can understand why Uka always goes back to him. Not just because he cares about Nina but because he just...loves a challenge. I think Cortex does too. Everyone leaves Cortex in the end, but you know who always comes back? Uka Uka.
I'd say N. Gin but I'm pretty sure he left at some point to do his own thing like Brio and the others did.
Cortex and Uka are both desperate, they're lonely and hate being told what to do by others like N. Tropy.
Lets be honest, Tropy is God tier. He could trap Uka and Cortex in a time loop if he wanted. He could do all this and that with how much power he has now that he controls time.
That is why Cortex doesn't have an interest in him though. He doesn't want to know the future, he doesn't want to constantly be told what to do by someone just to have the 'perfect life' he wants to do what he wants to do, that's why he's been avoiding him and telling Brio to take his calls for him. But Uka Uka on the other hand, he wants to help him that helps himself take over the world and get his revenge on his brother for what he did to him in the past.
Uka Uka has a hard time putting his trust in ANYONE( except Nina) to the point he's not even surprised anymore when someone betrays him. Other mutants have talked about him being depressed, lonely, self conscious about not having a perfect body that he starves himself (Supposedly they don't need to eat but it does have some effect on their power somehow) he wants someone so bad that he's willing to go back to Cortex even though he is the WORST person to put your trust in. It depends I guess, he has his days.
On a side note; I kinda miss the original concept of Nina being 6 or 5 years old because then the way Uka was being protective of her in the concept art makes so much more sense lol. It was also cute to see Uka being worried for Cortex's safety.
Anyway, Cortex and Uka? Not a perfect couple but it makes sense to me and that's why I love it. Just watching them struggle trying to figure themselves out and learning more about each other along the way, being more and more open to each other when no one's around or just a little around other people is interesting.
On one hand Tropy kind of helps Cortex but I can understand why he avoids him if he's just constantly on his case about everything he does.
Tropy:"Don't eat this amazing dish or else you'll be on the toilet for hours."
Cortex:"LET ME LIVE, DAMN YOU!!"
Something like that I guess or whatever. But also no one really trusts Tropy or Cortex all that much but they trust Uka Uka more...? That's interesting to know MORE about!! Is he in a way like his brother Aku Aku? Can he be nice? Is he more understanding than the rest of the evil genius's we know? Uka Uka used to be a good person back then but Cortex and the others grew up with bad people who for some reason just wanted them to be evil. So it makes sense that a lot of mutants like Tiny Tiger and others have more respect for Uka than they do for Cortex.