thanks for your interest in call-by-push-value. The fact that functions (all functions, not just lambda-abstractions) are computations is the main difference between call-by-push-value and call-by-value (where functions are values), and it does seem strange at first. But the mystery is (somewhat) resolved when you see the CK-machine, which is a kind of operational semantics that uses a computation and a stack. In terms of that machine, a function of type A -> B is a computation that aims to pop a value of type A and then behave as a computation of type B. For example:
print "hello again".
is a computation that first prints "hello", then pops x ("lambda" means "pop"), then prints "hello again", then returns x. And actually, the same phenomenon of "lambda" as "pop" is present in call-by-name; that's why call-by-push-value manages to subsume call-by-name.
I hope that helps! I should also say that the origin of call-by-push-value is that it was empirically observed within the models. The slogan was designed to fit the language and not the other way round. But that's just saying probably a less helpful answer, because it's just saying "the language is that way because the models say so".