The weather is warmer in Crimea. So it would make sense for Ukraine to wait until Spring. Right now it is damp and muddy so it wouldn't make sense to try to seize Crimea right now.
Putin’s ego is hyper invested in Crimea. It will be difficult to defeat the Russians there. Though Crimea needs fresh water from the mainland and this could be shutoff. Crimea is arid, believe it or not.
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Crimea is an arid peninsula with insufficient rainfall to meet the needs of its 2 million people. In 1971, the Soviet Union built the 70-mile-long North Crimea Canal to bring water south from Nova Kakhovka on the Dnipr river. The canal, which continues for another 170 miles to the eastern tip of Crimea, met 70-85 percent of the peninsula’s water needs, with most of the water being used for agriculture.
After the Russian annexation in 2014, Ukraine dammed the canal ten miles north of the Crimean border. Since then, Crimea has been drawing water from the aquifer, which is now running dry and becoming polluted. Climate change has brought decreased rainfall and higher temperatures to the region, exacerbating the water deficit.
https://responsiblestatecraft.org/2022/10/18/why-crimea-is-the-key-to-the-ukraine-war/