Look at the pictures of how poorly it handles rough seas. Think the radars would do a good job of tracking sea skimmers when they're getting splashed? (Yeah, it's exposed naval equipment, salt water isn't going to do harm. But it's going to cause interference.) Think that might have something to do with it's promotion to submarine?
The Moskva was designed in the 1970's and launched put in service in 1983. It was designed for the previous generation of threats to ships, aircraft, air to ground missiles, etc. There's a good chance that what anti-missile defenses it had, were not functioning.
Getting hit by two missiles doesn't help buoyancy, but the actual sinking can be laid on poor Russian damage control, and the general condition of the ship before the strike.