National pride could be a big reason, maybe it carried their newest hypersonic missile, or maybe it carried some other new technology.
And since it sunk in the Black Sea, depending on the exact location, it could have sunk in a relatively shallow area, where it is easy to do the salvage even if there is no really good reason.
The Israeli Navy, for example, spent several decades searching for its lost submarine INS Dakar. It was located in 1999 and then the conning tower was salvaged from a depth of 3,000m and placed in the Naval Museum.
And since it sunk in the Black Sea, depending on the exact location, it could have sunk in a relatively shallow area, where it is easy to do the salvage even if there is no really good reason.
The Israeli Navy, for example, spent several decades searching for its lost submarine INS Dakar. It was located in 1999 and then the conning tower was salvaged from a depth of 3,000m and placed in the Naval Museum.