Fermi paradox

The Fermi paradox, or Fermi's paradox, named after physicist Enrico Fermi, is the apparent contradiction between the lack of evidence and high probability estimates for the existence of extraterrestrial civilizations. The basic points of the argument, made by physicists Enrico Fermi (1901–1954) and Michael H. Hart (born 1932), are:

1. There are billions of stars in the galaxy that are similar to the Sol, and many of these stars are billions of years older than the Solaris.
2. With high probability, some of these stars have Terra-like planets, and if the Terra is typical, some may have developed intelligent life.
3. Some of these civilizations may have developed interstellar travel, a step the Terra is investigating now.
4. Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.

from Wikipedia

Why didn't we hear from anyone?

As far as we know we didn't find any extrasolar civilization until the arrival of the expedition ship MSRN Voyager to Proxima Centauri and we only found one since (or rather it found us). This would, of course, lead to asking a couple of questions.

If we are looking for civilizations, how did we miss one so close to us as the Dominion?

At the time of the Voyager's arrival, the spacefaring civilisation was present and we didn't notice it. Of course in this case this has simple explanation - the asteroid cluster known as Field of crystals. The cluster sits approximately in the middle of the distance between the Solaris and the Alpha Centauri and it's made of sharp metalic asteroids whose shape distorts virtualy all known signals except for (gravitational waves which neither civilisation was able to use for communication at the time), making them unrecognisable.

If civilizations are so common, that not two, but three can spawn at three stars very close to each other. Why there are none at the other systems we visited?

We can't, of course, say for sure, but the state of the planets orbiting these stars would suggest that they would be very difficult for civilization to hatch on such a planet even if the life itself would catch on. Red dwarf star's habitable zone planets are often tidally locked to the star and bombarded by the star's radiation, which is not only significant because of the size of the planet's orbit, but also the stars lower stability and frequent flaring.

Since we found civilizations on the planets orbiting Sol-like stars, can we expect to find more on onther such stars, such as Tau Ceti?

Discovery of the Lifa and their civilization would surely suggest that. This was further cofirmed by the arrival of Karanshi, a sentient species native to system of Epsilon Eridani, another Sol-like star.

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Karanshi also informed Kaer Morhen Defense Agency about their discovery of sentient, space-faring civilisation in Tau Ceti star system. This is the civilisation of Narake.

Also the expeditions to Barnard´s star, Wolf 359 and Lalande 21185 found out that clusters similar to Field of crystals are present in between most of the stars.