Abstraction & agility
I've seen some articles or comments alluding to a solution in which the façade caches URIs for later use. However, this runs the risk of treating every backend back-end URI as an entry point and would expose the client to the volatility of certain state transitions.
I've also come across a similar solution where the façade embeds back-end URIs as query parameters of its own URIs. This is an antipattern anti-pattern for a few reasons:
Finally, the examples given only integrate with one back-end service, but they the solutions apply to façades that integrate multiple services. In fact, one could quite possibly chose different solutions for communicating with each of them.