It doesn't make sense for Moff Periwinkle to turbolaser the continent to the bedrock if the tibanna gas mines go up with it.
Or Warmaster Grimdork can blow up Hive Factorius, but it won't be making him any tanks.
They typically use Base Delta Zero or Exterminatus as a last-ditch resort. Usually, it's limited orbital strikes with turbolasers set to minimal power or TIE Fighters/Bombers strafing at the enemy to assist the grunts on foot in taking objectives. They would only burn things down if everything is lost or the local leader is fucking insane. (see: Fyodor Karamazov and Ishin Il-Raz)
Another thing that I've come to hate about how they portray the Empire nowadays is how they make the Empire reward loyalty over competence-as if the Empire is content to be led by a cabal of buffoons whose only qualification is loyalty. If the trail of dead officers that Vader leaves behind is any indication, the opposite is true. Yes, you have exceptions like Ishin Il-Raz, but most of the officers in the Empire are rewarded for competence, not just loyalty. Many officers executed by Vader or the Emperor were fully loyal to the Empire, but their fuck-ups cause disruption among the troops and are therefore answered with death.
Meanwhile, this allows competent but disloyal people mask their ill intentions by being efficient and working their way up the ladder. People like Grand Moff Trachta, Grand Moff Bartam, Moff Kadir, Moff Kalast, Admiral Harkov, Sovereign Protector Carnor Jax, among others, had zero loyalty towards Palpatine and even betrayed him at some point. But they got to where they are because they were good at their jobs.
This is because the Sith culture which served as the tone in the top rewards results, not ass-kissing. Officers ass-kiss Vader and the Emperor all the time, but they'll still get killed if their fuck-ups are there for the Sith to see. Just as how, back in the ancient days, your Sith master doesn't give a fuck that you're trying to kill him, (in fact, he'd be greatly disappointed if you weren't) but if you fuck up in front of his peers and he becomes a laughingstock, you can expect him to string you up and blast you with Force lightning for an hour just so he can relieve his stress.
One thing about the Empire that is always emphasized is efficiency, and a nation cannot be efficient if all it has are butt-kissers who got to their post because they kissed the right boot. In fact, one can say that the Empire valued competence over loyalty too much, to the point where the moment Palpatine died on Endor, your average Moff, general, or admiral went land-grabbing and tried to claim a piece of the Empire for themselves, or they joined a faction that tried to enthrone someone to replace Palpatine. If they were truly loyal to Palpatine's legacy, they wouldn't have pursued such a self-destructive course, and they would've just crowned a friend of his or a relative, then gone back to fighting the Rebels as a cohesive unit.
It's the difference between Nazi Germany and all those tinpot Arab dictators. The Empire in the SWEU is the former, the Empire in Disney canon is the latter.