They also invaded the defenseless country called Afghanistan that was controlled by cavemen (and I'm being literal) spent trillions of dollars and were defeated and had to donate $100 billion to the same cavemen to buy their safe passage while they escaped Afghanistan in the worse way possible.
The United States can help the people of some country in the struggle for their independence, but they are not obliged to fight for them and will not. For twenty years the Americans have helped the people of Afghanistan with everything they could and even fought for them against the Taliban. But this cannot continue indefinitely. They trained the Afghan army and armed dozens of times more than the US has now provided military assistance to Ukraine. If the people of Afghanistan would give a worthy rebuff to the enemy, the help would continue. But they cowardly gave almost all the US equipment to the Taliban and surrendered en masse. Therefore, we have what we have. And there is no US fault here.
In contrast to this situation, the Ukrainians showed complete unity and mass heroism and professionalism in the fight against the Russian invaders. This causes a well-deserved respect and desire for them to help defend their country and their nation.