My initial thoughts are each SDK release the compiler and linker options are modified (over time) to take advantage of being more type safe/strict, and performant. It may take a fair bit of digging to compare between V8 and V10 code bases to provide an exact single answer to why. Though I would likely start by diff'ing the compiling/linking options used between versions and see if any options are related to improved handling of import/export decorations (since decorations have not changed much).
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