Why did the British Commonwealth make a guarantee to Poland that it could not keep?

This is a two part question: Why did the British Commonwealth make a guarantee to Poland to uphold their territorial integrity when they geographically could not keep such a promise and France was unwilling and lacked the military doctrine to take offensive action against Germany? Realizing that they were caught in a geopolitical vice with the U.S.S.R. and National Socialist Germany with the signing of the Nazi-Soviet Pact, if not before, why didn’t Poland allow a rail/road through the Polish Corridor and allow Germany to take control of the Free City Territory of Danzig which was 96% ethnically german? It was clear at that time after the Abyssinian War, Rhineland, Sudetenland, Memeland, Austrian and Czecho-slovakia occupation, that France and Britain politically couldn’t and militarily wouldn’t take offensive action against Germany and geographically could not directly help Poland.

Finland with U.S.S.R. and Rumania with Germany/Hungary/Bulgaria and the U.S.S.R. made agreements to give up some territory when they were in hopeless military and geopolitical situations, saving their nations from total destruction. Was the Polish Colonels decision logical and rational? It seems more realistic for the British and French to make a west wall similar to that of NATO with Norway and the Low Countries which could be supported militarily due to their geography and have more political support. Britain went to war to protect Poland, only to sell them out to the U.S.S.R. after the war. So, logically, what was the point for any of the nations to decide to fight it out? What did they gain? Poland was destroyed and Britain/France was bankrupted and lost their empires and standing as a world powers. Germany wanted to expand east, but could not occupy the U.S.S.R. with a population of only 80 million, mostly due to their ludicrous racial policies. At best they may have had a pyrrhic victory over the U.S.S.R. leaving them too weak to take on the west which, like in WWI, their military capabilities only grow over time while Germany would have been attritioned. I don’t see the logical or rational decision by any nation at the outbreak, but perhaps I have missed something. I would to hear others thoughts on this.

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Here is a response that made some sense.
Why did Britain and France declare war on Germany once Poland was attacked? Why was Poland so special? - Quora

In the end, Britain lost it’s empire for a part of the world that they could not possibly defend, and France was unwilling to aid with an offensive on German frontier in the Rhineland.

The possibilites of helping Poland were quite limited with the exception of a French invasion into the Rhineland, but they did not do it when the Rhineland was occupied by German troops, why would they do so during the Polish invasion? Again, I am not getting a good logical reason why the Western Allies made guarantees and declared war in an attempt to defend a nation they simply could not defend?

(1) How could Britain and France have better supported Poland against the Nazi invasion in 1939? - Quora