Even if you never need to scale it's cheaper to not have to physically maintain your own data center. If all the broken server, building power, building internet, access control, real estate costs... are all handled in the cloud there's savings there as well.
But those costs don't go away -- the cloud provider is going to charge you for them, along with a premium for profit?
I'm used to organizations moving out of the cloud when they realize that it's more expensive if you don't have very peaky load demands.
Very few people who don't use cloud use their own data centers. The dominant alternative to cloud is colo or managed servers.
And it's difficult to make that as expensive as a cloud deployment.
But that's somewhat negated if you lift and shift, because your application is not designed to leverage that capability in that way.