Does MDCA's DLP scan AWS S3 bucket contents to identify if any sensitive files uploaded ?

I have connected MS Defender for Cloud apps with AWS. However, if I check the Files section in the Defender portal, I would see S3 buckets as the folders appearing under AWS services. Contents of the S3 buckets are not visible. Moreover I had created a DLP policy to raise an alert if any sensitive file is been uploaded in the S3 bucket. I had uploaded the file but it didn't trigger any alert.  Why is it so ?