It’s pretty hard for them to reach with the weapons they have. Storm shadows can do it but it’ll take several, and at least right now, I suspect Ukraine gets more out of using them to go after depots and generals.
Also, they get some benefit to threatening the bridge without taking it out. Right now Russia keeps soldiers and anti missile systems protecting the bridge. Once it’s blown up Russia can send those things to the front.
I’m guessing they’re most likely to take it out after they cut off the northern route.