several reasons:-

1) It's a very LARGE rocky planet for the size of it's primary star - notionally only 30% of the mass of the earth, so in terms of the ratio of its mass to the star, it's maybe the largest rocky planet found to date (In formation terms, this could be seen as a failed gas giant, not big enough to accrete all that gas)

2) It is the LEAST massive planet found orbiting a main-sequence star.

3) It's method of discovery shows the value of continued and accurate observation of planets that have already been detected. Astronomers are going to be in business here for decades...

4) Even for a weak star, a large rocky planet has some life potential from internal heat and deep oceans. This planet, if compositionally similar to Earth, would have extensive volcanism and rapid plate tectonics, many subsea mountain ranges, and oceans about twice as deep as Earth's, so very few volcanic islands would break the surface. Simple life is possible without sunlight - driven by volcanic energy alone...