The 3-Clause BSD doesn't NOT release copyright. The copyright holder extends you a perpetual license to redistribute and modify the copyrighted work, provided you adhere to the license. They still hold the copyright. Without them holding the copyright, the 3 clauses would be meaningless, since they'd have no way to enforce them.

Releasing the license is commonly refereed to as "public domain", but it's not actually possible to relinquish the copyright in all territories, and therefore people generally prefer some kind of license.