I write this comment not to diminish the very real suffering caused by the current war, but as reminder of the destructive capacity of a full-scale industrial war, where the entire state is devoted to producing the means of war.
Not to mention that Russia has littered whole landscapes with anti-personnel mines, something which didn't really exist in WWI. Small, plastic mines, very hard to detect.
Imagine the industrial capacity of total war today...
Is the scale of the conflict simply significantly less, or is artillery more accurate(and has a greater range?) and therefore less shells tend to get used in a modern day context?
While artillery is still useful today as a cheap way to hit static targets with tons of explosives, modern combat has many more mobile units like tanks and armored infantry that are impractical to hit when they're moving around. Artillery is a big part of Russian military doctrine but no one uses it at the scale it was used in WWI.
Not sure what timescale you mean by "once" - if you mean immediately during WWI - well the story is a bit more complicated than that. The first tanks were tested in the battlefield in WWI, but they were few, rare, and slow. Some versions were effective at anti-trench warfare, but they didn't fundamentally change they war, because there weren't enough of them and they weren't that good.
WWII tanks were a whole different ball game, travelling at automotive speeds - easily 40mph - over most terrains, with much more effective armor from all sides, and both sides figured out how to use them effectively together with infantry and air power.
The WWI stalemate really got broken because the Allies - US, UK, and France - had a lot more in them, whereas the Central Powers - Germany, Austria, etc - ran out of manpower and supplies to keep up. They still made it hell on the Allies to gain ground, but they effectively had lost their ability to manage a counteroffensive through attrition. Tons of tactics were tried before that point to avoid an attritional war, but planes and tanks to make fast high powered strikes didn't exist (WWI planes couldn't carry much weight, so were ineffective as bombers, and had shorter range; they were mainly used as recon), and artillery was so destructive it hindered it's own slow advance.
Best source I've seen on these subjects is https://acoup.blog/2021/09/17/collections-no-mans-land-part-... and his followup article.
Mostly the US had a lot more in them, after sitting out the first 3/4 of the war.
WWII tanks started to force everyone to be a lot more mobile on the battlefield at which point artillery lost utility compared to the WWI era (though obviously still very useful)
And fun historical note, France definitely didn't get the memo, and were caught totally surprised by the speed of the Nazi assault. They were still using fixed phone and telegraph lines and their top commander wasn't even sitting by the phone. Their complete lack of imagination for how all the new technologies would change war was the main reason they blundered their defense so badly. Greatest victory the Nazi armies every won.
Artillery changes a lot once you have satellites and GPS and guided shells and drones, when the camera on your drone can point at something it sees and instantly turn that into a set of accurate coordinates that can instantly be transmitted to a battery that can instantly calculate a firing solution for those coordinates. You can fire one shell and achieve damage on target you'd need to fire dozens to achieve in WW1.
And this, along with the general technological advancement of war in every other way, means the scale is smaller. In WW1 you had to mass thousands of men in every kilometre because if you didn't then the enemy would, and overwhelm you with numbers. In Ukraine, whenever either side concentrates its forces beyond a handful of tanks and infantry squads, the other side hammers that concentration with accurate artillery as soon as they spot it. WW1 scale simply does not work.
Also, Russia has actually gained a huge border directly with NATO as a direct result of this war. It's really backfired in that regard. Finland wouldn't have joined NATO if Russia hadn't shown how dangerous they can be. They were perfectly happy with the status quo until this.
Launching a genocidal war for such goal is as laughable as all the other reasons that get stated.