‘What You Offer Has Zero Value’

I completed a book proposal and my agent had been trying to find a publisher for it for the last year.
Yesterday we met for lunch and she told me she is giving up on this book and that when I am ready with the next one, I can send a new proposal for her.

I asked her what does she think the problem is and she said that in the publishing world it means my book has zero value.

Since I finished this book, of course, I have been writing all along, working on my next book, but I am trying to figure out what lesson am I required to learn here, with this discomfort I have:

One option is to learn to accept the market’s judgment on the value I thought I was providing.
Another option is to keep looking for someone who will appreciate the value I created.

How do we know if we should give up on a product we created because several said it has zero value vs. keep looking for ‘my people’, that is the right publisher?