Massing men, machinery, or supplies in one place opens them up to attack by drones. Because of that, both the Russians and Ukrainians are relying on attacks by small groups of men and machines taking small areas of land at a time with a premium on transportation hubs and high ground.
There is also the problem with muddy ground that will soon dry up. A massive offensive might be waiting for the ground to harden in summer.
In any case, the Ukrainians offensive only took a few square kilometers of land. The current slow Russian advance has retaken that land and much more.
Both sides claim that the other side is suffering more casualties from this slow war of attrition. Regardless, even with the $61 Billion and the threat of French troops on the ground, the numbers are all in Russia's favor. They continue to out-manufacture and out-man the Ukrainians.
The angels might be on the side of the Ukrainians, but GDP and demography are on the side of the Russians.
The angels are not on the side of globohomo.