It all boils down to a small group of small creatures with limited intelligence
that has just begun to realize what it is and where it is in the scheme of
things, yet still clinging to its primitive, narrow, and amazingly egotistical
view that it is the Center of All Things, including the attention of its
deity and deities.

As a result, these amazingly tiny and short-lived creatures (they can't
even be seen from the nearest star system) continue to assume
because other beings aren't knocking each other down in an attempt to
get our attention that they assume these other intelligences therefore
do not exist.

And I continue to get more than a sense that these same Lilliputians
do not want there to be anyone else out there, at least nearby, for
fear of having done to them what most of them have done to other
members of their own species and Earth life in general of ages.

And yeah, how tough would it be to hide a probe from humanity? Not
very at all; in fact, you could have it dancing around in plain sight and
most people would assume it is some kind of gimmick advertizing a new
SF film or series, or that Halloween has come a bit early.