This is war and ground lines of communication are a legitimate and important target. And the Crimea bridge is on the top of the list for the following reason:

Russian military logistics is heavily dependent on railways, they were short on trucks even before the war. See, for example, this interesting article from War on the Rocks. [0]

By losing the railway connection, Russian soldiers in Crimea and Kherson Oblast can no longer be reliably supplied with anything. Tanks, fuel, you name it. Provisionally, ferries can be used instead, but the ferry capacity is a fraction of what a double-tracked electrified railway can carry, plus the previously existing ferries between Russia and Crimea were discontinued and sold after the bridge was put in operation.

The autumn and winter military operations have just grown a lot more problematic for the Russians. The only possible backup, a railway running to Donbas through southern Ukraine, is too close to the frontlines and likely to be cut by an Ukrainian offensive soon.

[0] https://warontherocks.com/2021/11/feeding-the-bear-a-closer-...