Does anyone know why it takes about 2 weeks for AY miles to post on AAdvantage?

Is this AY or AA's fault that the 'system upgrade' delay for so long?

I wonder how, the who inter-airline mileage work operationally... does the operating airline keep a log for 1/2/3/whatever day and pass them to the programme airline in batches? Or does it get fed into the programme airline's database immediately but the programme airlines update the accounts of their members in batches after a few days?