Why Email through Salesforce Marketing Cloud are not going out?

I have created one report on Lead Object in Salesforce and I want to send them Email through Marketing Cloud through Marketing Cloud Salesforce Connector. Previously, the email went out to all lead records. Why this time it is taking so long time to go out?

Tagged: Emails in Salesforce, Lead Object, Leads in Salesforce, Marketing Cloud, Marketing Cloud Connector, Marketing Cloud Emails, Marketing Tools, Salesforce Marketing Cloud