Planned line closure reasons

Sadly not, at least not in that much detail. Longer-term projects do get listed on the former, but most people aren't interested in the minutiae of what's happening (remembering that's why most of the TfL pages exist as they do).

There is an internal staff-only document showing the reason for closures (and timetables in operation).

By all means do open a new thread on the relevant forum if there's a closure you're interested in, and one of us should be able to answer it!