That would require the people making their interests known, which would never happen in practice. The reality is that most representatives are well-intentioned and try to do the job in good faith, but only the wealthy/corporations ever give them the time of day to tell what their interests are. The representative can only work with the information they have available.
When do you think the last time the average Joe talked to their representative to communicate their interests, as is their democratic duty? The answer is, unfortunately, half past never. A representative cannot represent someone who keeps their interests a secret.
"Never happen in practice" is objectively false given the civil rights wins of the past century. While incomplete they were real, and real change followed.
Starting with the premise that it's impossible won't improve society.
Maybe you have a certain story in mind, but the civil rights wins that everyone remembers were wins only after the people waited too long to make their interests known to their representative, completely boiled over, and threw themselves directly onto the fire to compensate. That is quite different to having regular conversations with their representative throughout the normal course of their lives so that the representative could regularly do their job with the full understanding of the people's interests.
You've pointed out something real, but it does not appear to be within the scope of our discussion.
When do you think the last time the average Joe talked to their representative to communicate their interests, as is their democratic duty? The answer is, unfortunately, half past never. A representative cannot represent someone who keeps their interests a secret.