Why is bacterial conjugation not considered to be a form of sexual reproduction?

It does not involve DNA.
No new cells are produced as a result.
It does not result in exchange of genetic material.
It only involves a single cell.

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.

yes, because even though a theory has a  lot of evidence to support it, it is not always true