Someone (Russia) comes to your house (Ukraine), rapes your wife, murders your children, robs you and then sells the stuff he robbed.
Wouldn’t you be concerned about that?
In conflict more often than not, the plunder has remained with the plunderer, despite near universal condemnation of the practice by some...... much of human history, armies plundered the vanquished as a matter of course and sometimes went to war solely to do so.
Ukraine is responsible for protecting what is of value to them. In this case the grain.