Question

what are the reasons of the existence of galaxies in the sky rather than scattered stars? ​

Answer 1

A galaxy far, far away

In 1923, Hubble found dozens of these variable stars in Andromeda, and determined their distance. He calculated that Andromeda must be at least 10 times farther away than the farthest stars in the Milky Way. ... Hubble published his work in 1929 and changed forever our view of the universe.

Answer 2

Answer:

No, not all stars are in a galaxy. They may have once belonged to a galaxy, but they are not a part of it any more. Some of these so-called "stellar outcasts" or "intergalactic stars" have actually been observed by NASA's Hubble Space Telescope.