If no driver accepts
We tell you straight away, instead of keeping you waiting.
It can happen that nobody is free at that moment, or that nobody accepts. When it does the app tells you, instead of leaving you in front of a request that waits for ever.
A car is never promised to you when there is not one. It is a choice: knowing straight away that you have to make other arrangements is worth more than a wait that ends badly anyway.
At peak hours and on weekend nights it is worth pre-booking. That is the moment when free cars are scarce everywhere, with any app.