boto3 describe_fleets api does not fetch all fleet information

I have created few ec2 fleet using boto3 create_fleet api. Now i want to see all fleet created in region for that i am trying to use describe_fleets. Here is snippet.

ec2 = boto3.resource(service_name='ec2', region_name='us-east-1')
response = client.describe_fleets()
print("result1:",response)
response = client.describe_fleets(FleetIds=['fleet-2342'])
print("result2:",response)

output

result1: {'Fleets': [], 'ResponseMetadata': {....
result2: {'Fleets': [{'ActivityStatus': 'fulfilled', 

If i don't pass any fleet ids it give me empty result. but if i pass fleet ids it fetch information.

Why describe_fleets without any argument does not fetch all fleet created in region ?