It's not necessarily anyone forgot they need fuel. It's more likely every readiness report filed in the past several years has said "everything is awesome". The

It's not necessarily anyone forgot they need fuel. It's more likely every readiness report filed in the past several years has said "everything is awesome". The reality being that nothing is awesome and actual readiness is a small fraction of what the paperwork says. So the general staff assume everything is awesome and they've got plenty of supplies and logistical ability. Now the disparity between the state of their forces on paper and reality become known. Even if the military planners assumed reported status was exaggerated by some amount, the reality is likely worse than that assumption. Keep in mind the Russians have been building their forces up on Ukraine's borders for months now, in winter. Even if everything was great that's a lot of food and fuel needed just for soldiers to sit around and more to actually conduct exercises. Then after months of burning through stocks of food and fuel they go on the offensive which takes even more food and fuel.