As to why the meetings took place in the United States, they wanted distance from Yugoslavia, so as not to give either side a perceived "homefield" advantage. Getting the meetings further from Europe was a good thing. Furthermore, major Asian powers did not take a real interest in the wars, at least to the extent that NATO did. That really left the United States as a good venue.

As to why Dayton was selected: it's not altogether accurate to say that the agreement was held in Dayton. They were not held in downtown Dayton, or even Dayton proper, but at Wright-Patterson AFB outside of Dayton. This was a secure location that kept the media at bay, something that the external powers thought was important to reaching a solution. The thought process was that less interaction with the media would force the parties to negotiate between themselves and not publicly towards an audience. In short, it brought privacy that a Washington DC or New York could not have. The Treaty of Portsmouth following the Russo-Japanese War is another example of a peace treaty being signed in a relatively obscure locale.

Dayton ended up providing other benefits that likely would not have been realized in larger cities. There was a real enthusiasm for the peace process, and the residents were excited to be at the center of such an important event. There were vigils for peace, and the local news media took an intense interest in covering the talks. This probably did not figure into the planning, but was certainly a nice added bonus for the talks.

For more, check out any of Richard Holbrooke's books. The Road to the Dayton Accords is very interesting, and provides an inside look at this process in much more detail. To End a War is also really good. Of course, its important to remember that he isn't always the most modest in his tellings of the story, but there is still quite a bit of really fascinating history in all of his accounts.