Here's a unbiased experts opinion from Colonel Markus Reisner, "
The Ukrainian army has learned from its mistakes since the annexation of Crimea,” says Markus Reisner, colonel in the Austrian Armed Forces and head of the development department at the Military Academy in Wiener Neustadt. Back then, the Russian army was inflicting massive casualties on Ukraine “just by being able to shell them with their artillery in the open.” This time it’s different.
The army command in Kyiv deliberately shifted the fighting to urban areas in order to be able to entrench themselves better. “Only in this way was the Ukrainian army able to survive,” Reisner emphasizes the importance of this tactical decision. Linking military necessity with the applicable international legal situation, the outrage at the Amnesty report becomes understandable.
For the Kremlin, on the other hand, the report is a welcome gift, says Markus Reisner. “Such reports are of course used for propaganda purposes and in the struggle for information sovereignty in this war,” he is certain.
So in other words, the Russians don't have much of a choice but to use siege tactics. Also it's important to remember this is the only way Ukraine can survive, but they can't have their cake and eat it to, so they bitch and whine that they are entitled to use this illegal tactic. Well they are actually denying using this tactic, but one can read between the lines.
https://germany.detailzero.com/world/57206/Amnesty-International-raises-serious-allegations-Did-Ukraine’s-war-tactics-really-endanger-civilians-–-Politics.html