Hi Shan,
At BI level extrcation only is not the work, there are lot of back end jobs daily may run as per the business needs.
If your basis person, i think you can easily anlyze why this much growth happening on daily with help of db team.
otherwise take DB team help and monitor one day. they can find where/how the data base increasing day by day.
check and implement below options:
1. if possible delete the PSA, change tables with requried apporavls
2. is BW team performing compression?
3. if any used cubes/dso are theren, try delete with help of approvals
4. deletion of SLG1 logs which old 90days
5. reorganising logs
Thanks