They only get sent out if you have not yet made your picks. If you have made your picks, there is no reason to send out a reminder. THe entire purpose is to alert those who have NOT yet set their picks. And of course, they are only sent out to those that are in the specific pool. Each Pool sends out its own alert reminders.
Also, they have to be enabled per individual:
On the picks page, this is what it looks like when you have the email reminders ENABLED (you click the Disable Email Reminders link to DISABLE them).
On the picks page, this is what it looks like when you have the email reminders DISABLED (you click the Enable Email Reminders link to ENABLE them).
btw, I am OPEN to adding some additional functionality to this. Its been the same since day 1 (4.5 years ago). If there is something I can add/modify to make it easier for people to figure out, then I am all for that. Also, if you think it would be good to send alerts even if they have made their picks, that could be an OPTION (either global or per individual). Feel free to create a thread in the Pickem suggestions forum if that is the case