Most likely the build up of those beta amyloid is faster than what the brain can clear by itself. The drainage likely just reduced the amyloid significant enoug

Most likely the build up of those beta amyloid is faster than what the brain can clear by itself. The drainage likely just reduced the amyloid significant enough for the brain to recover. This is likely more of physics explanation than biological. It is similar cleaning the wound by itself has spectacular effect for recovery than you leave it cluttered with dirt and pus.