Please change need to enter master password every two weeks.

Qutrit

Three main issues I can think of off-hand:

1. The bar for adding a preference is pretty high. If you do a search of this forum for "add a preference" you can get some idea why (tl;dr there are hundreds of requests for various preferences).
2. Doing so would add complexity to the lock service. This is not ideal for a number of reasons. For example, complexity can lead to mistakes, and mistakes are the last thing anything wants in their password managers lock service.
3. If such an option existed, inevitably someone (multiple someones) will enable it either for themself, a loved one, a friend, a colleague, their boss, ... and then that person will forget their account password as a result. That isn't something we want to encourage by building such a feature.

Ben