It was implemented for two years after the war.
The Morgenthau Plan, which was a long term political plan, had opposition against it among both US government. What was implemented, was the JCS 1067, a short term military doctrine. Morgenthau wasn't happy of such diminishing of his ideas.
Firstly, how do you explain why the allies refused to allow German goods to be sold for food?
Short answer: By not assuming malicious murder attempt.
The long and thorough answer:
This whole subject is not my "special interest" so inaccuracies might be around, but I tried to fact check things and names.
You are probably referring to the policy of controlling Germany's recovery to avoid repeating revanche politics of 20s and 30s. Allies were not thrilled by an idea of Germany having even a remote chance to rebuild its war industry. There was also an attitude of blaming and punishing the German people for Hitler, so they were not considered to deserve same prosperity. So the purpose of plans and doctrines was to both to avoid a new arming and to make sure that German's standard of living wouldn't be better than European average, ie. to keep Germany so weak that it wouldn't consider a new WW3.
For these things, Morgenthau suggested that the new Germany should be an agrarian country. Main focus would be in developing the agriculture to feed its people, and dismantling the heavy industry permanently.
JCS 1067 was a set of instructions to the US military occupation, that followed the same logic (but different motivation) of developing the agriculture in a minimum amount that was needed to keep famine and following civil unrest away, and to not pour US resources to the country that was supposed to be left to a civilian government following a short occupation (yes, it is always about the money - US was still a little bit isolationist at that moment, but that changed after the war). The industry wasn't going to be totally destroyed as in the Morgenthau's original plan, but it wasn't going to be allowed to produce more than what was needed to upkeep the society (political decision for those above mentioned purposes).
Of course, it wasn't that easy, and USA (and allies) became quickly aware that they couldn't just "upkeep the society until there is a civilian government". Agrarian Germany couldn't work without any income from exports (or from pockets of USA, who was the only one that could afford such extra costs). There wasn't enough land for the population (hence, that "if Morgenthau plan would have been followed..."). And, of course, Germany's own natural resources (coal) were needed in the whole Europe. So they had to start developing surplus production (against the doctrine of JCS 1067). This change of policy started as soon as mid-1945. Last restrictions were removed around 1946 or 1947, when a whole new doctrine JCS 1779 was introduced. Marshall Aid followed 1948.
Here's an additional catch about that buying the food thing:
Things happen slowly. Neither agriculture or industrial production can appear immediately. Recovery takes years. Because of this, the Europe was rationing until 1947-1950 depending of the country. The rationing means that the sales of rationed goods both domestically and internationally is restricted until the supply exceeds the minimum demand.
So there wasn't even food to buy, and that was a global problem. US didn't supply food from its own supplies only to Germany, but also to other European countries (hence, rationing meaning not enough supply even for their own demand). US had a good production surplus (after all, there wasn't any war in USA), but it wasn't that good that it could feed the whole Europe. Hitler's Nero Decree (scorched earth tactics) left Germany in 1945 worse than what other countries were (in Germany it turned to a massive figurative suicide pact with no intention leaving anything behind after Hitler's regime), so the need for food was and remained even more severe (it didn't help to limit any industrial production to fill only domestic needs). The population to feed was about same as France and UK combined.
One could equally say: "Man-made German Famine Denial".
You just did a motte-and-bailey argument by changing wording to more accurate "man-made famine" from the "murder through starvation"...
Difference is that the holocaust and the course of WW2 events are clearly documented. Planned genocide of German population is not.
BTW, my mother told me that she had no problem obtaining food during the war.
No wonder. The war economy didn't collapse until late-1944 when the war was moved to Germany's soil. Before that the rationing and imports from occupied areas made sure that most people could keep living as usual.