We live in a world where everyone wants everything to come easily and be easy. Unpublished authors berate agents for not having uniform guidelines that would simply allow them to shoot out one query letter to everyone, and published authors are seeking the magic promotional item that will hit all potential readers in the same way and make them buy books.
It’s never going to happen. Uniform submission guidelines mean that you’re assuming all agents are exactly the same, and thankfully that’s not true. We all have different tastes and different ideas. We love different types of books and different authors, and thankfully so.
If you really want to succeed when it comes to finding an agent or getting new readers, then you constantly need to be re-creating and rethinking your strategy to appeal to many different types of people. What works for one might not work for you, what works for one of your books might not work for the next. What works when charming and wooing one girl is not likely to work with another and what works on that girl one night, might not work the next.