Additionally, the thought that we're not alone and we're not the most advanced species. If that's the case, then why haven't a more advanced species made contact yet?
For the same reason that humans have not "made contact" with ants.
Why do you assume a higher intelligence would even be capable of making contact with us on a level we understand? The discussion would be meaningless, in the same way that an ant would not comprehend our desire to build a freeway right next to their ant hill.
That doesn't mean there isn't one right in front of our eyes though.
If there were, I would expect us to be carelessly crushed in a short period of time.
The history of biology is discovering species in places previously thought unlivable: impossibly salty environments, volcanic vents, etc. A natural extension is finding species in places "above" humanity.
b) Maybe they have no way to reach us. Despite sci-fi speculation, we still have no reason to believe the speed of light is not the ultimate speed limit of the universe.
c) Maybe they don't care. Aliens in movies often come here to invade us, eat us, steal our resources, etc. But, if any species had the level of technology to come all the way here with a force large enough to subjugate us, they wouldn't need to. Far more resources than they could take from this planet are already freely available floating around in space much easier to take.
d) Maybe they're so different from us that they don't even notice we are anything. Maybe we wouldn't notice them either.
(b) I agree. We have all reasons to believe it is not possible to accelerate something with mass to 'c'. We know this with astronomical levels of certainty. Anything that changes location without acceleration is either pure energy or pure fantasy.
(c) I agree. Even Dyson spheres don't have the raw energy capture to move an Earth of resources out of the sun's gravity well. Perhaps an Earth has rare and valuable resources that are quickly expended, with high value per kilogram. But there's no reason to believe an Earth would be special. The only real reason aliens have to contact us are the same reasons they'd try to immediately genocide us to get us out of their way anyway.
(d) this is an entire field of xenospeculation, but high energy rockets are really bright and very probably the only way to get to a different place in space. You pretty much have to talk microbe scale to go unnoticed in space.
[Edit, misread point b]
There's no reason to believe it would have to accelerate for all its curse.
> You pretty much have to talk microbe scale to go unnoticed in space.
There are myriads of stars we know nothing about, planets being discovered; and dust clouds only detectable because they are unbelievably huge.
Any craft capable of moving things in our medium size realm or larger will glow. If you want to direct your exhaust along a cohesive line, you're basically talking lasers. And those can't really provide much thrust power.
If the hypothesis is that there are interstellar civs out there that don't exchange beings or materials, it's pretty hard to call them interstellar.
I'm basically talking about a propulsion system that we haven't imagined yet. Because nothing we've (realistically) imagined would make an interstellar civilization possible.
I didn't say they wouldn't exchange beings or materials at all. I'm just saying that individuals will not be hopping in their space cars and cruising off to the crab nebula for the weekend.
Granted this isn't a 100% proper analogy because a lot of these tribes have been contacted prior and have knowledge of the outside world. Yet it could be as something as simple as that; if there are far more advanced species we could be simply left to our own devices on purpose.
#4 is probably the biggest problem. Digital compressed broadcasts would be difficult to detect, and by the time you have that technology you can build much more sensitive receivers and don't waste energy dumping millions of watts into space.
There could be 1000 intelligent species in the Milky Way right now and it is still unlikely any would visit our solar system within the past 10,000 years, nor in the next 10,000 and we would not be able to detect their faint compressed, encrypted broadcasts.