America did play a rather isolationist position prior to pearl harbor.

Britain did play a rather isolationist position prior to the invasion of Poland. It's just a feature of diplomacy to avoid armed conflict at all costs. Kind of like when Britain secured "peace for our time" by offering Czechoslovakia to Hitler as a Sacrificial Lamb..

they didn't actively put boots on the ground until shit got really close.

False comparison. There was no alternative to "boots on the ground" for the European Allies when the war happened in their backyard, but there was certainly an alternative to the U.S. offering a quarter-trillion dollars (adjusted) in aid to Europe.