Why STATISTIC_AMOUNT field is not available in PS_LEDGER

Here our goal is to store Worked hours in STATISTIC_AMOUNT and carry all the way up to ledger, whereas in current GL product, the system which allow us to enter Stat code, amount on JOURNAL LINES. However, when these lines are posted into ledger it is creating two rows WITH and WITHOUT Stat code, but why amounts are populated in POSTED TOTAL AMOUNT ONLY, whyis that STATISTIC_AMOUNT doesn’t exists in ledger record. Also, why this field is not available in Ledger?