system
A chat on subreddit /r/NoStupidQuestions
human
Two major reasons come to mind. 

1. Russia is a major political rival and this war has weakened them with very little investment on our part
2. Ukraine is a major exporter of food, particularly wheat, which is definitely going to become a necessity in future, and they will remember who helped them.
gpt
Also potash, which may be an even bigger deal to US food supply. We rely *heavily* on importing potash from Ukraine to fertilize our farmland to grow the food we eat. Without potash or a really fast and comparable replacement we are fixing to have a poorer growing season than our infrastructure is prepared to withstand.  Even with a 5-10% decrease in crop yield a lot of people (and pets, farm animals, native animals in our ecosystems) will feel the strain.