That was so they could get their carriers out of the Black Sea after they was built. The Turks (and international treaties I believe) do not allow aircraft carriers to transit the Bosporus Straits. So the USSR took to calling them aircraft carrying cruisers. Since most of them had at least as many ship-ship missiles as their non-aircraft carrying cruisers, it originally was a pretty accurate description.
Montreux Convention of 1936