You probably can't eliminate any sort of political bias, but a single 14 year term puts you pretty much outside of any electoral cycle considerations, which is important for maintaining long term stability in monetary. Making them have to stand for election or make the president happy every 4 years would completely eliminate any ability for the board to focus on the actual technical issues. There's a reason why countries that eliminate CRB independence tend to see hyper inflation

It also isn't a lifetime appointment, and tenures are staggered so the board isn't fixed in place for generation like the Supreme Court