Boto3 CloudTrail API returns empty response

I am running the following code and I can see CloudTrail events in the console and also comes in the cli ( that means I using the correct token ) but the response is empty. What is the wrong in the code? Though I didn't need all regions but ran the code through all available to see if I can get response from any of the regions.

This cli provides output aws cloudtrail lookup-events --lookup-attributes AttributeKey=EventSource,AttributeValue=sts.amazonaws.com --max-items 10

But this code does not. The commented lines does not make any difference if uncomment them.

import datetime
ec2_client = boto3.client('ec2')
response = ec2_client.describe_regions(AllRegions=True)
for reg in response['Regions']:
    print (reg['RegionName'])
    try:
        ct_client = boto3.client('cloudtrail', region_name=reg['RegionName'] )
        response = ct_client.lookup_events(
            LookupAttributes=[
                {
                    'AttributeKey': 'EventSource',
                    'AttributeValue': "sts.amazonaws.com"
                },
            ],
            # StartTime=datetime.datetime.now() - datetime.timedelta(minutes=10000),
            # EndTime=datetime.datetime.now(),
            EventCategory='insight',
            MaxResults=30,
        )
        print (response)
    except Exception as e:
        print (e)```

Resolved after removing EventCategory.