Because central planning to fairly and sanely distribute resources for millions, or billions, of individuals requires a depth of calculation that is humanly impossible.
Marxism, or any system of mass control or manipulation, only requires direct management and maintenance of a relatively small number of people. There is no need to try to be fair or sane with 99.99 percent of the population. They are to be bullied, killed, fooled, etc., through the actions of the small number of people who are directly controlled.
When you hear the term, "Central planning doesn't work," you need to add, "If we are striving for ethical, humanitarian outcomes." That's generally the issue when people have the central planning debate: managing resources to produce the most benefit for the greatest number.
If the goal is to maintain a political elite who can kill, rob, oppress, etc., at will, central planning is pretty simple.
Want DP delivered to your inbox daily? Subscribe here: