Even within Poland a lot of people disagreed with it.

Pilsudski's plan relied on many, many countries coming together to coordinate. Here was the problem.

Pilsudski pissed off Lithuania when he waltzed into Vilnus/Wilno and claimed it for Poland (as it as his hometown).

Ukraine was in a civil war, and they were suspicious of the idea as it was likely to result in Polish hegemony, like under the Polish-Lithuanian Commonwealth. Ditto with Belarus.

Latvia and Estonia had little interest in falling under a Polish hegemony.

Germany and France were extremely suspicious of Pilsudski, and would likely have frustrated his attempts to create this federation.

The Soviets also opposed it and actively sought to frustrate his attempts.

Lastly, a large chunk of Poland opposed it, preferring instead to occupy territories that were historically Polish or could be easily Polonized.

Source:

Davies, White Eagle, Red Star