Yep, wiring
I'm owner #3 and it seems to me that owner #1 was pretty meticulous about most things on board, including wiring, based on the underlying work here. But then owner #2 has "added" a few things and perhaps not been as particular with routing cables, labelling, using tinned wire etc.
This pic is from 2018 and I'm slowly removing unnecessary wiring (seriously I have a bag of about 12 kg of it so far) and replacing the domestic/household cable with tinned wire and numbering everything.
The rat's nest on the floor of this cabinet has improved but is still not finished.
Like Zzzzz says, if the circuit still works, other stuff gets prioritised above it.