This is a question that Google support would be better suited to answer, as they have more insight into the inner workings of their form submission system. However, it's possible that your form was flagged as inappropriate because it violated one or more of Google's terms of service. For example, your form might have contained offensive or obscene content, or been used for spamming or phishing purposes. If you're not sure why your form was flagged, you can contact Google support for more information.