Agents only agree to represent writers when they think that they have a better-than-average chance of selling their books.
Agents work as literary matchmakers, pairing the right writer and book with the right editor and publisher. They also know which publishers will not suit, and when not to submit.
The publishing world is finite. Most books will suit only a handful of publishers, and good agents know that there is little to be gained by submitting beyond that small circle.
So if you are newly represented, and your agent only seems to be submitting to a small number of editors, they are probably doing their job properly despite your worries: but if you're still not convinced, you could always talk to them about it.