1) Because munitions can only be used once, and they need more munitions to continue killing more Russians;
2) Putin has apparently decided that if he can't defeat Ukrainian soldiers, he'll just keep killing you Ukrainian civilians. And even if his army has lost all offensive punch, they can still use aircraft and artillery to shell civilian areas.
This isn't complicated. Winning or losing, armies need to be supplied continuously.
It is mindboggling that all the snarky “then why do they need help” FReepers don’t grasp the concept of resupply. It doesn’t say much for their IQ.