i read somewhere tht because of how not many humans would join they ended up recruiting aliens. unless im thinking of sith troopers which I doubt
"As the ranks of the Stormtrooper Corps were steadily replenished with enlisted troopers from both Human and Non-Human sources alike, the Empire's once heavy reliance on clones diminished over time, mainly due to the loss of Kamino and other various worlds that held cloning facilities.[30] In addition to the highly expensive operation of consistently producing clone soldiers, the practice was complicated by two other reasons—the most effective clones that were grown in the Kaminoan-fashion took too long to reach full maturity and the fast-grown Spaarti clones were of extremely poor quality."
This is what i found
"The new practice of recruiting Non-Humans as stormtroopers was continued by the Imperial Remnant. Over a century after the fall of the old Empire, the Remnant eventually reformed itself into a new Empire that was protected by stormtroopers composed of Humans, Near-Humans, Humanoids and even Aliens that hardly even resembled the Human anatomy standards. Non-Human stormtroopers were not the only new additions to the Empire's resurgent army, however; Human females became more common within the stormtrooper ranks by 130 ABY."