Why did Poland share its Enigma research with Britain and France in 1939?

Poland shared its Enigma research with Britain and France in 1939 primarily because the Polish Cipher Bureau, led by Gwido Langer, realized they were becoming overmatched by increasingly complex German encryption methods.1

By late 1938 and early 1939, Germany had added new scramblers and increased the number of plugboard cables, raising the potential key combinations to 159 quintillion. The Polish bureau lacked the financial resources to build the significantly larger number of bomba machines required to counter these advancements. Furthermore, with the threat of a German invasion becoming imminent following the withdrawal from the nonaggression treaty, Langer acted to ensure that the critical progress his team had made would not be lost to the Nazis. By providing the British and French with spare Enigma replicas and blueprints for the Polish bombas, Poland ensured that their foundational work could be continued and industrialized at Bletchley Park, ultimately proving vital to the Allied war effort.1