The Soviet-Japanese Neutrality Pact was not signed because they bloodied each other's noses and were done. It was signed because both sides knew they were about to go to war. The Soviets with Germany and Japan with the US. Both sides were eager to secure their flank from the other.
On the Japanese side there was a debate between a northern and southern strategies. The army backed Hokushin-ron aimed at China, Manchuria, and Siberia. The navy backed Nanshin-ron aimed at Indochina and the South Pacific.
Khalkhin Gol spelled the decline of Hokushin-ron, but it took some time for this to be fully abandoned, for the navy to gain supremacy, and for tensions with the US to reach a boiling point.
The Soviets and Germans had no illusions that the Molotov-Ribbentrop Pact would hold. Hitler was very clear about his contempt for the Slavs and plans to expand eastward. The Soviets were eager to delay the coming war with Germany as long as possible to give themselves more time to prepare, something made very acute after their humiliation in the Winter War with Finland. The Germans wanted to secure their Eastern flank while they were stomping around Western Europe and Scandinavia, as well as secure valuable resources that would be cut off in the inevitable Allied blockade.
The Soviets were riding a knife edge with Germany. On the one hand, there were talks of the Soviet Union joining the Axis in late 1940, but these went nowhere. On the other hand, German and Soviet paranoia meant any move could be seen as hostile. A Soviet treaty with Japan could been seen as strengthening ties with the Axis, or it would be seen as securing their flank in preparation for war with Germany.
Once Japan joined the Axis in late 1940 it became more clear that a treaty with Japan would be seen, publicly anyway, as a gesture of goodwill and peace towards the Axis. The Soviets ultimately decided to negotiate a treaty. Meanwhile Germany had already decided to invade.