Not everybody is online. SMS reaches any phone in Nigeria, which makes it the right backup for reminders, one time codes and campaigns to older or rural customer lists.
Not every customer is on WhatsApp, or on data. SMS reaches any phone.
What your customers already do on WhatsApp, Instagram and Facebook, handled in one place and priced in naira.
Most businesses need both. Using the wrong one is how you either waste money or miss customers.
Use it for reminders and codes, and let WhatsApp carry the conversation.