If I printed something in my flow, why can't I see it in my logs?

quoting the docs - you just have to add

log_stdout=True

Prefect tasks natively support forwarding the output of stdout to a logger. This can be enabled by setting 

log_stdout=True

 on your task.

@task(log_stdout=True)
def log_my_stdout():
    print("I will be logged!")