More and more agents are looking for the disgruntled. Somewhere out there are authors with agents, but they're not happy about their agent's performance. For whatever reason, they haven't clicked, or the author thinks the agent is too busy to spend much time on their next project. If that describes you, then query away on your next project. If you haven't been published yet, don't even bother.
At the Ashley Grayson agency, they no longer want to hear from the great masses of writers who don't have a novel already on a shelf somewhere. It takes more time to sell something that is not a sure thing. Without a track record of sales, an author is a risk to take on. An agent could push a manuscript to every editor they know and come up empty. A lot of time and expense gets put in and nothing comes back in return. There's a limit to how much of that any agency can afford.
Al Longden left Rights Unlimited and went off on his own, but he's not looking to pick up some potential star. He wants the best he can find, so that he can make some money straight away and not have to worry about paying the rent when all the cash is going out rather than coming in. Surely there's a few authors out there who would like to switch agencies, and Mr. Longden is waiting by the phone for your call.
Wishing that someone at Jane Rotrosen's agency would take on your supremely polished debut novel? If wishes were horses, beggars would ride and you could claim the likes of Andrea Cirillo as your personal representative. This being the real world, and one that is cold and cruel, you are out of luck. Ms. Rotrosen's agency will only accept queries from those who have made the grade previously.
Not only is it getting more and more difficult to get a novel published, it's getting increasingly hard to land an agent to represent you so that you have a chance to get published.