When a visitor to your event's page registers for the event, a Campaign Member record is created for the Campaign related to the event you've linked within Soapbox Engage's Events app. Since organizations might have different ways to define the status of these Campaign Members, the Events app does not apply any particular Campaign Members status value. Instead, following standard Salesforce conventions, the new Campaign Member is given the default status value.
This is great news for Salesforce administrators, as it provides you the control you need to customize whatever you'd like to set as the default Campaign Member status for every Campaign you create. After you create your Campaign in Salesforce, just click on the Advanced Setup button on the Salesforce Campaign page in question. Then, after clicking the Edit button, simply choose or create the proper status value you'd like to have selected as the default and click the proper Default checkbox as you see fit.
Happy event management!