Magento 2 Product Alert out of stock notification email

Question

Does anybody know how does the Product in stock notification email triggers to the subscribers?
I already have the cron job set up and I do see the catalog_price_alert cron being successfully executed in the cron_schedule table.
Everytime the catalog_price_alert cron being excecuted, nothing happens. No emails were sent.
My SMTP is working fine. All my order and customer emails are going out normally.
Please someone help!