Why has my domain renewal not done automatically?

There are numerous reasons as to why this can happen.

These days, most registrar has an auto-renewal feature which means you can buy the domain, set-it-and-forget-it.

That is until your card on file expires. But registrars also has a process in place to remind you to update your card details months in advance before renewal.

If for some reason that you decide auto-renewal is not for you, you will have to manually monitor the domains, and set calendar reminders for yourself.

If you did not set the reminder, and you forget about it, your domain renewal will not go through.

And none of the reasons above has caused your domain renewal to not have been completed, you will have to speak with your registrar to find out what had happened.