Many of the answers were somewhere between "technically correct, but misses the point" and "completely inaccurate". One answer I'd like to shout out is the one that points out that hot dogs (aka Vienna sausages or frankfurters) are actually beef sausages, at least a lot of the time, and at least in the U.S. Nathan 's, Sabrett 's, Best 's Kosher, Vienna Beef, and the list goes on. Even companies that make frankfurters of all kinds do all-beef varieties (Ballpark, Oscar Meyer).

However, in addition to candor, the questioner has a point. Why aren't there more non-frankfurter sausages made with beef anymore? Well, let's address a few points. (I'm going to discuss the U.S. market, because that's what I know.)

Economics. Ground beef sells much more than ground pork in the US. When you break down an animal, you get a couple things. First, you get the best cuts of meat (rib eye, filet, and carpaccio from cattle, and tenderloin, ham, and belly from hogs). Then there's the secondary, or stew meat. (Front leg (aka picnic ham) and rump for hogs, and front leg, shoulder and brisket for cows.) Then some other cuts, and some extra fat, and that's the grinder. The major cuts almost never stop. The grinder almost never grinds. The intermediate cuts, well, it depends on the market. The butcher will sell all that the market will bear and grind the rest because the unground product is more expensive and saves labor. However, you end up with a lot of ground beef and ground pork.

In fact, ground beef is far more popular than ground pork in the US. Just go to the grocery store and look around. There will be three different grades of ground beef in many different package sizes, maybe two to three one pound packages of ground pork. People use ground beef for burgers, meatballs, lasagna, chili, all sorts of classic American favorites, and it's the predominant thing that the hot dog industry buys. Meatballs and meatloaf also have ground pork in them, but it's usually just an addition to the ground beef that provides a little moisture in the flavor. But secondary cuts of pork aren't all that popular either. Do you eat a lot of chuck stew? Do you buy a lot of pork stew? The loin gets cut into ribs, the ham gets smoked, the belly gets made into bacon, and the shoulder doesn't move. Sure, some of it gets barbecued (which is the preferred choice for pulled pork), but that's a regional practice. At the end of the day, there will be more ground pork in the market, but nowhere to go. Sausage is the perfect home for it. I would say that there are so many pork sausage ingredients in the market that pork products would crowd out the other sausages on the shelves.

Unique properties of pork protein. Well, I'll spare you the science, but the texture of the sausage relies on a network of proteins. When cold pork proteins are stirred with salt, the proteins break apart and form long strings that wrap around each other. This creates a three-dimensional mesh in which small pieces of fat and moisture are encased in a matrix. Ever notice how the texture of the sausage meat sticking out of the tube doesn't resemble hamburger meat at all? You know how you make a pound of bacon and then you get a skillet full of grease? Sausage has almost as much fat as bacon, and when you cook a pound of sausage, most of the fat doesn't move. That's why when you take a bite, you get a juicy flavor. Other proteins (poultry, beef, lamb) also form this matrix, but not as easily. This is why in many cases when someone wants to make lamb or beef sausage, they still add about 1/3 pork just to improve the flavor. However, this doesn't happen in the case of kosher beef sausage or halal lamb sausage because the religious ban on these butchers prohibits pork.

The unique qualities of lard. Lard is solid at refrigerator temperature and solid at room temperature. It is solid at body temperature. It doesn't really melt until 140 degrees. That's why high-fat beef turns into crappy tartare. If you take a big bite of a slightly warm beef sausage, the fat will form a waxy layer on your palate without bursting into juicy juices in your taste buds. If you have a kosher sausage, you really need it to be hot! This isn't a problem for hot dogs or bologna, because in these types of sausages, the fat is held in a stronger emulsion along with the protein and moisture, but that's probably too esoteric. However, lard is solid at refrigerator temperature, begins to melt at room temperature and is liquid at body temperature. This is why high-fat pork is incredibly delicious. It's also why a chilled pulled pork barbecue is better than a chilled brisket barbecue.