It's not about the shoes
Runna automatically tracks the "running miles" of your shoes. This gives you an incentive (new shoes) and an overarching trackable goal.
This is an important nuance: counting down the remaining miles of the lifecycle of a pair of shoes, is not the same as counting total miles ran.
Lifecycle = counting down, the Goal Gradient Effect (you get closer).
Total miles ran = counting up, you're keeping a tally with no set goal.
They could have an arbitrary target like "run 1,000 miles", but it lacks the incentive at the end.
i.e., you get to treat yourself to a new pair of shoes.