So Ukraine would waste bombs (and potentially planes) bombing essentially useless targets…when they could be bombing tanks or logistics points or bridges or a convenient command tent filled with generals.
Kyiv knows that they would loose a lot of support from the West.
Ukraine has a legal right to hit back inside Russia, but is currently not being permitted to do so by partners whose support Kyiv cannot afford to lose.
The US and others have placed limits on acceptable targets for the arms they provide, while also demanding assurances from Kyiv that these weapons will not be used inside Russia itself.
More like it, they are afraid Russians will fight harder if the war is on Ukraine’s soil. Right now all Ukraine wants, needs is the Russian soldiers out of their country.