Why was the USSR called a big construction site?

It so happened that industrialization in the USSR began later than in Western Europe and the United States, therefore, in the 1930s, factories were built in the country in huge numbers. And this is against the backdrop of the economic crisis in most countries of the world (1929-1933). In the 1940s, the country’s rear was rapidly developing during the Second World War, and after the war the country was rapidly recovering.
In the 1950s and 1960s, economic growth rates were high, and massive construction of housing and oil and gas fields began in Siberia. Thus, many cities were built literally in an open field (Norilsk, Nizhnevartovsk, as well as Togliatti and Naberezhnye Chelny).
You also need to take into account that the USSR had a planned economy, and it assumed zero unemployment and the constant construction of new factories. As well as late urbanization (in 1928, the rural population predominated), so the peak of housing construction in cities fell on the period from 1954 to 1989.