Simon/Simeon, Zebulon/Zabulon, and Isaac once were quite common names in America. Take a look at this book, mostly lists of soldiers during the Revolutionary War. Search for "Simon", "Simeon", or "Isaac" and there's virtually one instance on every page. "Zebulon" and "Zabulon" were less common, but were nonetheless common enough that there are dozens of instances of the name as well. "Asher" was rare, but not entirely absent, while "Gad" did not seem to have any popularity.

Among Revolution-era people with those names are Isaac Low (signer of the Articles of Continental Association, who later turned Tory), Isaac Sears (an American Patriot during the war), Simon Boerum (a political leader from Brooklyn during the war, after whom the neighborhood of Boerum Hill is named), Simeon Rockefeller (whose descendants later on became one of the wealthiest families in the United States), and Zebulon Butler (political leader in Connecticut).

Later on, during the War of 1812, there was Sir Isaac Brock (a Major-General for the British killed in action) and Zebulon Pike (a Brigadier-General for the Americans after whom Pikes Peak in Colorado was named, also killed during the war).

All these names went out of style later on. A sociologist or social historian would probably be able to better tell you why names in general go in and out of style, and perhaps why these particular names did.

One possibility is that these kinds of Biblical names became increasingly associated with country bumpkins or "hillbillies" after the onset of the Industrial Revolution in the mid-1800s. There's a 1993 documentary called The Unknown Marx Brothers in which Chico Marx's daughter Maxine posits that her uncle Zeppo Marx gained his stage name because of the popularity of "Zeke and Zeb" jokes about Midwestern country folks in the early 1900s, at a time when the New York brothers had temporarily moved to Chicago and proved to be terrible farmers.

Whether or not the actual origin story is true (Zeppo himself claimed it had to do with zeppelins), "Zeke and Zeb" jokes were certainly a real thing, something of the "redneck" jokes of the late 1800s and early 1900s. A cursory search of historic newspapers turns up such humorous stories as reprinted in the August 18, 1904, edition of the [Brookville (Indiana) Democrat] (http://imgur.com/8J8rSJK) and an "old story" in the March 5, 1943, edition of the Amarillo (Texas) Globe Times.

To this point, there were a couple of country musicians in the first half of the 20th Century named William and James Grishaw. They took the stage names of Zeke and Zeb Turner, an obvious reference to the old country "yokel" jokes.