Why does an element with absolute "fall out" of the flow?

Because with position: absolute the browser stops accounting for the element in the flow-building algorithm. Document flow is a system in which elements affect each other through their size and position (as with block, inline, relative). But absolute turns this mechanism off.

#What happens technically

1. the element does not participate in calculating the size and position of its neighbors;
2. the browser does not reserve space for it: it is as if it does not exist in the overall flow;
3. its position is determined only by coordinates (top, left, right, bottom) and by the positioned ancestor.

#Result

• neighboring elements behave as if this block does not exist;
• the absolute element itself overlaps others, occupying only visual space.

Summary: an element with position: absolute "falls out" of the flow because the browser excludes it from normal flow placement and treats it as an independent object positioned by coordinates.