You'll notice there are a few different types of events (Volunteer Opportunities and Events).
Events: By default the "impact settings" are turned off so hours are NOT being collected. Normally the usage for events is to "track" the following: attendance, signups, RSVPs, etc.
Volunteer Opportunities: By default the "impact settings" are turned on so hours are being collected and tracked. Normally the usage for volunteer opportunities to allow for foundational metrics to be captured.