Star Wars: Why The Empire Didn't Last Long In Canon (But Did In Legends)

screenrant.com:

The Book of Boba Fett acknowledges the short-lived reign of the Galactic Empire in the canon timeline, and there are several reasons why this isn’t the case in the Star Wars Legends continuity. In “Chapter 5: Return of the Mandalorian,” Din Djarin, now the owner of the Darksaber, speaks to The Armorer, who chides the Empire for lasting only a few decades while the Mandalorian culture continues to exist after over 10,000 years. While the Sith Lord and Emperor Palpatine cheated death via the dark side of the Force and ingenious contingency plans in both continuities, the specifics and timing of his plans, as well as technicalities resulted in canon’s Galactic Empire falling much sooner than its Legends counterpart.

When Palpatine died during the Battle of Endor in the canon timeline, his contingency plans, such as Operation Cinder, were enacted immediately. Numerous worlds, including those who were loyal to the Empire, were brutalized and Imperial forces regrouped and converged on the planet Jakku, where they fought the fledgling New Republic in one final battle. The New Republic prevailed and the Empire formally surrendered, dissolving not long afterward by the New Republic.

Related: Why Palpatine's Clone Return Was Better In Legends Than Rise of Skywalker

While illegal Imperial holdouts continued to exist, as shown in both seasons of The Mandalorian, the fascist regime no longer existed in any official capacity by 5 ABY. As shown in the Star Wars sequel trilogy and sequel-era non-movie material, the Empire continued to live on in different forms. The survivors of Jakku fled to the Unknown Regions and formed the First Order while a resurrected Palpatine and the Sith Eternal built their forces in secret on Exegol. This is