The Polish did not want Soviet help, the Soviets had in fact warned the Polish on numerous occasions about German intentions, and had sought an alliance against Germany with Poland’s primary friends France and the UK. While the latter were certainly reluctant, Poland was adamant in refusing in cooperation with the Soviets, which included denying them access to help Czechoslovakia in 1938. The real reason for which turned out to be the Poland also wanted some of the action and demanded Zaolzie region.

Poland was not exactly friends with neither the USSR nor Germany, but they still favored Germany. For example, following the Soviet-Polish war which ended on Polish term, they decided to be the opposite of magnanimous, they did not try to normalize relations, and as the leadership changed from Lenin to Stalin, the Polish did not react, it took a full decade before the Polish felt ready to sign a non-aggression pact with the Soviets in 1932. In contrast, when Hitler came to power, the Polish signed a non-aggression pact almost immediately, and further did so with personal notes between Hitler himself and Piłsudski. A courtesy they never offered to Stalin despite over a decade of attempted normalization, and the fact that Stalin hadn’t written a book where he literally called Polish people subhumans who was an atificial state that shouldn’t exist who’s population he was going to displace or enslave.

As I previously mentioned Poland went on to essentially sabotage any attempt at Soviet military guarantees for the neighbors of Germany against Hitler, including Poland itself. After 5 years of futile attempts at establishing such an alliance, and Polish refusal for cooperation, the Soviets gave up and conceded that German expansion was now inevitable including into Poland and eventually the USSR.

They were faced with three scenarios:

Germany takes all of Poland and it’s resources, and is that much closer to Moscow following the annexation. Poland is split between the USSR and they gain a buffer against the inevitable war with Germany in the future, while also reclaiming millions of Belarusian citizens who were lost in the Soviet Polish war, and denying resources to Germany, as well as the opportunity to reclaim other territory lost in the Russian civil war (Romania, Baltics and Finland). The Soviets immediately engage the German army after it is done fighting Poland, likely ensuing in a prolonged military conflict in which England and France will do nothing help the USSR, following years of conflict and millions of dead, England and France will finish off Germany, occupy it and the USSR will get nothing except casualties. It should be obvious that choice was barely a choice at all, there never was any option to help Poland against Germany, and frankly in the 1930s it’s hard to find a less competent and more deluded foreign policy than the Polish one, I don’t think there is an outcome which was possible at the time, which could have been worse than the one the Polish chose. They wanted to not fully ally with any of their neighbors, Piłsudski is quoted as saying: “Not with Moscow or Berlin, but above Moscow and Berlin.” I.e. we won’t make friends with anyone, we’ll make enemies of everyone.

I cannot reiterate this enough, they still chose to be more friendly and approachable with the guy who wrote a book about how he was going to kill them and destroy their nation. Polish foreign minister Józef Beck said “With Germany we risk our lives; with Russia we risk our soul.” What they meant with this was that the dirty communists might repress the catholic church, which was of course far worse than the Nazis killing everyone in your country, provided you’re the worst politician in the 1930s.