Funny I find this NOW cause I was just ranting about this with @honeylief on Discord.
The running idea is that there's "Empyrean" and "Titan's Blood."
We know titans EXIST within Rise. Cough, cough, the Crying Titan in the Series Finale. We ALSO know that a Kraang skeleton was found there, alongside- well, who would have thunk it, EMPYREAN. Which is used to. Ya know. Almost murk Splinter and turn him into a proper, bootleg Casper.
But, that raised a question: Why would a Kraang Skeleton be hanging around a Titan Skeleton?
Unless, my dear friends: The now dead Kraang infected the Titan's Blood.
Going on a small sidebar here: In both Hades and The Owl House, Titan's Blood is seen as this extremely powerful yet limited resource. It's ripped straight from the very beings who breathed magic and life into the world in the first place. Titan's Blood can be used (in Hades) to permanently upgrade a weapon. In TOH, it's quite literally the thing that allows the Wayward Witches to gain a small sliver of their magical strength back, just by being NEAR it.
SO, I am going off a similar thing with my headcanon.
Titan's Blood is a resource that is naturally found within MOST Hidden Cities. When the locals say "The city has a heart beat," they're being serious. The Titan's heart is still beating underneath the city, and its blood is the entire reason why the Yōkai have remained out of sight! The Titans of Old are STILL protecting the Yōkai race, even though their bodies have long grown still.
And yet. Yet. We KNOW the Kraang visited the planet once before. We KNOW that the Kraang somehow made it down to the Hidden Cities, or else that corpse would have not been there!
It's infected Titan's Blood.
A whole new type of magic that, while granting the possibility for growth, changed, and untapped potential? If it's not treated properly, it can drive somebody to the brink of INSANITY.
Thus, brings me to how the Rise Brothers are different than those who got infected by the Oozesquitoes.
The Rise Boys were PURPOSELY created. They were made with the intention to be war machines. Meaning: Draxum most likely worked with that batch of Empyrean for who knows HOW long. He made that batch SPECIAL. He needed it to be as refined as possible in order to produce the war machines he needed. Throw in a great human fighter, and BOOM. Four war machines, ready to go with very little imperfections.
However, with the Oozesquitoes? They were much less refined. The Empyrean used for them? Draxum probably didn't spend as much time fine-tuning the process! Thus: A poorer quality of Empyrean (Aka, INFECTED TITAN'S BLOOD.)
Just my idea on why villains go. Well. VILLAIN mode. Because the version that mutated them wasn't nearly as refined as the batch that mutated the Rise Brothers.
( @sooahbites @kayden-chr @bluemooneagle01 @lartiel @adrifyadrift cause you guys enjoy my world building rambles)