the answer is relevently obvious in my opinion Adolf Hitler disliked communism and stalin wasnt all to much of a fan to fascism
Just prior to the formation of Tripartite Pact, the Soviet Union was informed of its existence, and the potential of its joining.[1] Vyacheslav Molotov was thus sent to Berlin to discuss the pact and the possibility of the Soviet Union joining it.[1] For the Soviets, they considered joining the Tripartite Pact to be an update of existing agreements with Germany.[1] On Molotov's visit, he agreed in principle to the Soviet Union joining the pact so long as some details, such as Soviet annexation of Finland, could be worked out.[2] The Soviet government sent a revised version of the pact to Germany on November 25.[2] To demonstrate the benefits of partnership, the Soviet Union made large economic offerings to Germany. It was around this time the Soviets would not make commitments to invade British territory in Asia that Hitler stops considering a push into the Mediterranean in 1941 but instead thought to deal with the Soviets first.