Mixpanel’s Insights and Explore reports show different types of data. Insights displays Event data sent to Mixpanel using the mixpanel.track() operator, while the Explore report displays people data sent to Mixpanel using the mixpanel.people.set() operator.
In order for these counts to show the same value, you’d need to add a condition requiring that a People Profile be created for every user who performs an Event. You also may have fewer People Profiles shown in Explore if any profiles have been deleted (either individually or in bulk) at any time.
The fact that these reports don’t match is not necessarily a problem. You may be creating People Profiles for registered users, while collecting Event data for both registered and anonymous users.