Note that that "66%" actually means 8 of the 14 Avenger-class mine countermeasures ships we have (57%)... and that the number was bumped from 4 to 8 back in March. 4 more are based in Japan, with the remaining two in San Diego.
Considering that the only reason we have ANY minesweepers is for use in the Persian Gulf, that is understandable.
We used to have 12 Osprey class minesweepers that were built in the early 1990s (commissioned 1993-1999, just AFTER the Avenger-class), but those have all been sold off... the Avenger class (commissioned 1987-1994) are the only dedicated minesweeping/hunting ships in the USN!