Second. Attention is finite over a day

Presence takes effort, and effort is a limited quantity that runs out. A person running at the edge of their capacity has nothing left to bring to an act that requires being present, and being present is exactly what khushu asks for.

So sleep debt cashes out here. So do illness, a newborn, a parent you are caring for, two jobs, a commute, and the six hours of scrolling that a bad week produces.

None of that is a spiritual diagnosis. It is arithmetic.