Question

Why did world leaders follow a different plan for reconstruction following WWII than the one used following WWI?

Answer 1

The reconstruction plan after WWI did not work, and actually it can be argued that it actually led to WW2 - for example through the fact that the Treaty of Versailles left Germany poor and vulnerable to extremism.

So since the first plan did not work, the leaders decided to follow a different path after the next war.