Data loading into PSA when extracting from Heterogenous systems

Hai there,

I have a question regarding the extracting from Heterogenous systems. When extracting data from non -SAP systems for example getting data using DB connect, xml, flat file etc. why is the data loaded only to PSA? Is there any specific reason for that or is it because you can administer and debug before loading into ods or cubes?

Thank you very much for your time.