Why do you think scientist have decided that conjunction is not a form of reproduction

Conjugation is not considered a form of reproduction because it is not a prelude to reproduction at all.

Completely new genetic information is being exchanged between cells, changing the cell's characteristics. Bacteria often do this to resist antibiotics. If humans did this, one would become their own child, and then their own grandchild and so forth with every conjugation. Of course, this is highly infeasible in a multicelled organism.