A good lesson here…
When aspiring authors hear something like, “I’m sorry, but I’m just not passionate enough about this project to take it on,” they tend to take that very personally. But it’s not a judgment on your work. It’s a sober-minded distinction, a reminder that ultimately this is a business of perspectives and subjectivity. “Not passionate enough” does not equal “you suck.” It equals, “It’s not my cup of tea.” Period. Full stop.
A lot of folks also get bent out of shape by the “not passionate enough” argument because they feel that the commercial potential of their work is so obvious and so enormous that passion shouldn’t matter. “I don’t care if you’re passionate, you Philistine! Don’t you want to make gobs and gobs of money? Aren’t you passionate about that?”
Again: This business is subjective. You need and want an agent (or, indeed, an editor) who is as in love with your book as you are, someone who will take care of it, look out for it, shepherd it safely through the dangerous valleys and gullies of the publishing world.
Look at it this way: Would you rather have a babysitter who cares deeply for your child…or just someone willing to take your money?