Having an agent also frees you, the writer, to do what you do best. The agent's job is to find the right house for your work, and once successful, to negotiate the best deal for you. An agent can also provide you with encouragement and validation. Writing a good book proposal, then sending it to the appropriate editors is basically all you have to do. Most are used to working with unagented writers.
Agents are always on the look out for new talent.
That's how they earn their living. The agent is just too over-commited to take on any new writers. You have approached the wrong agent for your genre. It pays to do a little homework first. Writer's Digest Books publishes a market guide to literary representatives.