Nigerians are very funny people, so that registration process is very necessary. I run an online shop, and we had people placing "test" orders on our live site. We would call to confirm the order, only to find out the number either does not exist or that the owner of the number does not know what we're talking about. Turns out people were using random phone numbers to place test orders, just to see if our website works, or to see if we would deliver, or for any of the other malicious reasons they could think of. When we started phone number verification, fake orders disappeared. Nobody puts their real phone number in a fake order.
Unlike us, Konga can't call to confirm every order. This is not scalable for them as they're much bigger than us. Their only bet is to do automatic phone number verification. Sometimes people also make mistakes when they provide phone numbers during checkout and then there's no way to contact them (80% or more of Nigerians don't check their mails, and a majority don't even know their mail password, so depending on emails as backup is useless). Konga's registration process, in my opinion, is not very tasking. It's as easy AF. The phone number verification is done in-page not like you'll need to leave and come back, or click a link in your phone. As we all know, there is a disadvantage to everything, but I think phone number verification and registration before checkout solves more problems than it creates.
I also need to mention that Jumia calls to confirm every order. Test, in my opinion, is not scalable. If they intend to be the Amazon of Africa, they can't keep doing that. Secondly, I hate phone calls. I prefer to verify my number the Konga way.