It appears that one potential goal is to take out the air defence, show that they can destroy the Kerch bridge but leave it intact, then deny fresh water into Crimea (it comes in from the west). This puts them under siege, with a path out still, and a deadline.

Just targeting them gives Russia propoganda and makes the Russian people think Ukraine is evil and resist them. That’s not what you want. Forcing them to leave still makes them scared and costs them money, and it forces them to spread the message wherever they end up. This is a much smarter move.