Why isn't past service expense considered operating expense under GAAP?

Isn’t this from adjustments based on services employees have offered in the past? If not operating, is it financing then? And would it be difference under IFRS?

In US GAAP, past service cost is recognised in OCI and amortized for service life of concerned employees. To the extent amortized, it should be treated as operating expense. IFRS does not differentiate between service cost n past service cost, both r expensed.

one of the problems in the cfa practice test does otherwise. It only considers the current service cost as part of the operating expense and doesn’t consider the amortized section at all

I think that this is a simplifying assumption but be ready to include them if the questions asks you to.