This is gonna be a bit long, so the TL;DR is because he's a bad person.
Put simply, Helix does everything for his own benefit. Pretty much just read the "Neutral Evil"
article on TVtropes or your handy RPG core rulebook of choice, and you won't be far off. He is that alignment personified.
There's plenty of principled or philosophical bad guys on Chaos and in media in general. People with creeds or religions or some reason to do things beyond "it was for my benefit or interest at the time". Most IRL bad people, however, are bad in large part because they are selfish and unempathetic. There are other reasons to do bad things (lots of ideological bad guys IRL too), but as someone who's spent a lot of time around bad people for work reasons, my observation is that they're almost all compulsively selfish. This is Helix, and it occasionally makes him a little uncomfortable to write.
Helix will use laws, break laws, keep agreements, break agreements, make friendships, break friendships, or do anything and everything else if it benefits him. He doesn't even care much about faction or ideological lines in others. A Jedi that stays out of his way is better than a Sith that doesn't, and he'll cheerfully work with that Jedi to solve a common issue or remove a common threat. Anyone and everyone of every imaginable loyalty is a valid buddy or ally, as long as he benefits in some way.
He is, in short, an ultra-egoist. "Anything I do is correct because I'm the one doing it."
Everyone else mostly falls into two categories: a tool to be used, or an obstacle to be avoided or removed. It's all very impersonal, very sociopathic. Rare is the person that can escape these categories and become something else to Helix. There's a low single-digit number of people who have.
Of course, as I've been increasingly showcasing, sometimes he does bad things for no apparent gain. This has been a growing theme in his recent actions.
The supreme kicker being that Helix is cruel partly because of his ability to absorb or assimilate the personalities and memories of others. He has done this to, at this stage, tens of thousands of people, and it has affected his reasoning.
All that human or humanoid cruelty, stupidity, hatred, bias, selfishness, and short-sightedness focused to a single white-hot point. That's Helix. He is malicious on a level that is difficult to quantify, yet also very petty. Not the guy who'll take over your planet, probably not the biggest threat on the board, but one of the very last people imaginable that you want to be at the mercy of. After all, he's got a small city's worth of experience and imagination to pull from.
Of course, people are more than the bad, right? Being a Sith-aligned person, a lot of his victims/constituent personalities have been largely good people. He actively chooses not to engage with that part of his consciousness, because he is fundamentally a bad person. Evil by nature, maybe, but mostly evil by choice. He could be empathetic, merciful, brave, altruistic, etc tomorrow if he wanted. He could probably even be very good at it, as his understanding of the universe and its underlying principles is astounding, appearing to be magic to many. He could cure disease, end hunger, and maybe single-handedly drag up the galaxy's standard of living a few percentage points. Instead, he uses his considerable intellectual and material gifts to cause suffering and enrich himself.
If he has anything like a redeeming trait, it is a sympathy with weird, offbeat, outcast or broken people. He's one himself, after all. He gathers such people to himself as much as possible, genuinely likes them, might even mildly inconvenience himself for their sake, but if the chips are down and it's himself or them, he's not picking them. For reference, watch the recent HBO series about the Penguin to see what this type of person thinks and acts like. Selfish affection isn't really affection.
Helix is basically just everything stereotypically bad about human behavior, dialed up to 11 and given the power to indulge it all to the fullest. He can be very thoughtful or introspective, but any moral or philosophical underpinnings he cites to you are probably window dressing or a manipulation tactic. If you cite any of yours to him, he will file them away and use them against you later if necessary. In his eyes, needing to justify your actions is the refuge of inferior beings, and what is philosophy if not the art of seeking justification? If you're going to do something that others might see as evil, do it, own it, and do it with some panache, he'd say. Don't make excuses or pretend there's justice in an uncaring universe. As an aside, this is why he's all-in with the Sith. They tolerate this type of individual better than most.
All of this in mind, what primarily motivates him is independence. He wants complete freedom of action for himself while not caring overmuch about the freedoms of others. His assets are almost entirely fleet-based, his technology is all proprietary and jealously guarded, all to be as non-dependent on others or their resources as possible.
I don't think he could retire or do anything else even if he did want to. War and destruction are all he's known, and probably all he ever will know. Even if he succeeds and plucks the last credit in the universe from the last bank, kills the last possible threat to his interests, he'd find new stuff to pointlessly fight over. You know what they say about living the sword, though.
