Cost of course. Mostly the cost of the crew. Not just the cost of a couple thousand sailors, but also the cost of training people to run them. It's not like there are a whole lot of people left in the Navy who ever served on a BB. With only so much money to go around, choices have to be made.
If I recall the cost of a Battleship at sea for a year was less than what is spent on one Space Shuttle mission.
I would rather have one less space shuttle mission per year and keep a battleship