The reason is mostly for activation. You have less signups, but more active users as 1) people who care enough to signup stick around more, and 2) with an email

The reason is mostly for activation. You have less signups, but more active users as 1) people who care enough to signup stick around more, and 2) with an email you can reactivate users later on. I’m not saying this is right or wrong, just that these numbers are really well tracked.