There are several reasons abandoned cart reminder emails not being sent from your website.

It could be that WP-Cron is disabled on your site, or your server has some restrictions which does not allow WP-Cron, or the emails are actually sent, but the email server has failed to deliver them to the recipient. If you see the emails under the "Sent Emails" section but if they are still not being received, then it’s likely a problem with your email server. You can contact your web host about this.

You can refer to this post for fixing the WP-Cron issue.