Your argument for the no-contact is :
-Alien are way beyond us (ants). But hey, we study ants at least. That's called the 'Zoo scenario' (we're the pet).
Some other arguments are:
-They stay in their Dyson sphere, happy with their lives without any need to conquer the galaxy.
-They communicate by means beyond our understanding (Snowden used that argument by saying that aliens use encryption)
- We're part of the alien: Earth was randomly seeded with life because aliens found it the fastest way to populate the galaxy.
The best one:
- Everyone stay silent, because there are some killer robots or something out there. (Ancient Aliens need a ton of episodes about that)
Other arguments are mostly about death:
-Life is ultra rare
-Life is fragile ( this article argument's)
-Sentience is doomed (to kill itself before take off)
All this is so fun