Keeping coordinates hidden to protect wrecks from looters is not an unreasonable policy to set, they'll do even more damage to the marine environment to harvest copper, bronze, low-background steels and memorabilia.
I think we do have the capability if wanted, it just does not make economical sense.
Basically we'd need to filter the gases injected to the process to guard against contaminants, which would cost a lot. So it's just cheaper to recycle old steel.
Low-background steel, also known as pre-war steel, is any steel produced prior to the detonation of the first nuclear bombs in the 1940s and 1950s. Typically sourced from ships (either as part of regular scrapping or shipwrecks) and other steel artifacts of this era, it is often used for modern particle detectors because more modern steel is contaminated with traces of nuclear fallout.
Very interesting. Wiki also says it's not needed for most uses now since that background radiation has greatly reduced since we stopped blowing up bombs in the atmosphere.
"... background radiation has decreased to very near natural levels ... low-background steel no longer necessary for most radiation-sensitive applications,... However, some demand remains for the most radiation-sensitive applications, such as Geiger counters and sensing equipment aboard spacecraft. For the most demanding applications even low-background steel can be too radioactive and other materials like high purity copper may be used."
