When I launched myself onto the writing world 50 yeas ago in England I had no problem finding an agent. Now with nearly 30 books published, 14 novels and about the same number non-fiction under two different names I find it difficult o get an agent to show sufficient interest (or courtesy) to even answer an email. I am left wondering what exactly agents require and who has perpetrated the myth that without an agent a writer cannot hope to sell their work? Un-agented I am selling more than I ever have and other writers I know are also doing well on their own. Our only regret the precious writing time wasted Emailing agents who don't want to know about us.
Well, I'm not sure that I care for your tone ...
But I'll answer anyway. I've said before - more than once - that not all authors need agents, so it's certainly not me who's perpetrating that myth. One could presume that it's likely agents who say that all authors need agents, the same way lawyers say that everyone needs to sue (and before you protest, law is my background so I know whatof I speak). It's better for business if everyone thinks you're indispensable. Some authors need agents because they want to have someone manage their career/give creative support/generally chat to them about 'stuff'. And, in truth, it's often publishers who prefer that authors have agents - or, rather, that authors submit to them via agents - as they'd rather agents read the slushpile and find the Next Big Thing.
I find it curious that you have been trying to interest an agent in your work considering the success you've had without one. What would an agent offer you at this point? I'm not saying an agent couldn't offer you anything, but as you haven't mentioned why you're now looking for an agent, I'm curious. If I were an agent receiving a query from you (and for all you know, I have), that's what I'd be wondering too. But the main reason why I may not think I'm the right agent for you is that you may not be writing books that are right for me. Agents have their individual tastes the same as any other readers, and if your books aren't to my taste I'm not going to take you on, no matter how many books you've had published, because I wouldn't be able to represent you properly. In the past I've cynically taken on the odd project thinking it would be a winner, even if the material didn't appeal to me - I'd think that I could identify a large readership for that story and thus I should just put aside my own tastes. It's never worked. I've never once been able to get those projects over the line because my heart wasn't in it. And most agents who've been agents for a while have worked that out too.
Somewhere out there, there's an agent who'll love your writing - if, indeed, you still want an agent. The trick is - just as it is for unpublished writers - finding that agent. Being published is not necessarily a guarantee of finding an agent. I've turned down published authors several times, for various reasons. Sometimes one of the reasons is that I don't think they need an agent.
Finally, though: if you really, really don't need an agent ... why are you writing to me?