Viz Media now releases 4 Case Closed (detective Conan) manga per year, why?

I have done my math and Viz Media used to release 6 Case Closed (Detective Conan) manga per year (or one every two months) until recently they have changed it to 4 per year. Now knowing the math that I know it will take another 8 years to catch up with Japan! Whats the deal? Have they gone down in popularity? Does this mean the series is close to ending? (Which I wouldn't mind since Japan has about 70 now) Why the change?