There seems to have been some policy miscommunication between political and military parties of both nations.
The US has maintained that the restrictions have been to not allow offensive use, or specific long range missiles for targeting well inside Russian territory.
Ukraine understood this to mean using them to fend off an attack, and only targets within a specific distance from the border.
In the past few months it seems that much of this has been clarified, and Ukraine is now using US munitions for a proper US “preemptive defensive action inside enemy territory”, because a Russian base in Russia is full of Russian soldiers who will be ordered to attack, therefore an attack is defensive.
If it was an actual miscommunication or a pivot is unclear, but the US language seems to have not changed, and a policy that acknowledges that almost anything Ukraine does in this war is inherently defensive is much more reasonable.