I've used Blue Water Dive Travel, which KathyV linked earlier, for a Galapagos trip with good results. Caradonna and Maduro are mentioned from time to time. I think the Scuba Board Invasions and Surges like to use Bay Adventures.
I don't use travel agents for simple, straight forward trips outside the pandemic in the Caribbean, where arranging flights and booking direct with the dive op. and hotel (if need be) is easily done.
But for a trip abroad, such as to the Galapagos, where I'm not familiar with what legs of the journey need to be made, the hotel choices to stay at, when it's wise to show up early and spend the night, how to go find the boat, etc..., they come in handy.
I don't use travel agents when flying in the continental US, but when traveling abroad there's one thing I really appreciate - the ability of travel agents to book all my flights on one ticket. At least that's been my experience, even for international flights involving different airlines. When I am flying outside of the US I've never been able to do that; I have to book each flying leg of the trip separately.
That doesn't sound like a big deal until you run into delays with one flight along the way; I learned that one the hard way. If your flights are booked separately the other airlines don't know or care if you are delayed. But if they are all booked on one ticket, the next flights are notified and they will automatically make adjustments for you as needed.