All working knowledge has a decay curve of usefulness. If you rely on having up-to-date, deep technical knowledge as a manager, you will eventually lose the thing that makes you effective. From personal experience, this happens after 6 to 12 months from when your primary activity becomes managing people.
This is especially bad for managers that try to make technical decisions themselves—it works until it doesn’t. The results can be truly bad when the manager doesn’t know they are far out on the decay curve.
What can you do about it?
For managers, it’s a lesson in delegation and leadership. Support others with the right depth of technical knowledge to drive the decision and manage through them. Stay involved but moreso to apply good judgement—delegation not abdication. It’s possible to stay close to the details but try not to fool yourself into thinking it is at the same level of proficiency.