Compartmentalization doesn't create knowledge gaps, but incompetence does. In the corporate world the incentives aren't aligned well. You get promoted for delivering business results instead of good solutions. Most corporate middle managers defer their responsibilities to their employees which is why you end up having to know so much and do all the legwork of asking around. Lucky you that's a lot of power they're just giving away. Oh hey so that's why any random low level employee can leak so much information! Who woulda thunk it?
Assuming they became your boss through technical merit they should be able to adequately describe requirements and anticipate implementation details. They could do it themselves if they had the time, but they don't anymore. Good requirements shouldn't need follow up questions beyond you potentially not knowing how to do something. You ask your boss.
Your boss doesn't have to know the whole project to deliver their piece. This funnels all the planning towards the top and they have massive incentive to shut the fuck up and not leak anything. It really is that simple.