¿Por qué no les dio Lupe el dinero a Uds.?
In English, this sentence means:
Why didn't Lupe give money to you?
Why do we need to put "les" in this sentence?
¿Por qué no les dio Lupe el dinero a Uds.?
In English, this sentence means:
Why didn't Lupe give money to you?
Why do we need to put "les" in this sentence?
¿Por qué no les dio Lupe el dinero a Uds.?
The majority of the native speakers I talk to say it sounds better and clearer with the "les", which, by the way, is an object pronoun, and is already indicated by a Ustedes. Deleting "les" might possibly render the sentence agramatical.
Please take note that "les" is not reflexive because it refers to "you (plural)", and Lupe was the subject of the sentence.