it isn't though. Wealth distribution isn't the aim of communism, just inevitable effect of it. And as such it don't have to be exactly equal. Quoting Lenin:

The abolition of classes means placing all citizens on an equal footing with regard to the means of production belonging to society as a whole. It means giving all citizens equal opportunities of working on the publicly-owned means of production, on the publicly-owned land, at the publicly-owned factories, and so forth.

Also Marx:

In a higher phase of communist society, after the enslaving subordination of the individual to the division of labor, and therewith also the antithesis between mental and physical labor, has vanished; after labor has become not only a means of life but life's prime want; after the productive forces have also increased with the all-around development of the individual, and all the springs of co-operative wealth flow more abundantly – only then can the narrow horizon of bourgeois right be crossed in its entirety and society inscribe on its banners: From each according to his ability, to each according to his needs!

As you can see total equality is neither achievable nor desirable under socialism and meaningless under communism.