I think part of it is that restaurants make things differently, especially in the USA, and sometimes blog recipes reflect that. In a lot of restaurants they throw a bunch of stuff that’s available to bulk things up.
There’s a supermarket chain here called La Sirena and they have food courts and the sancocho is actually quite good. I usually get it if we eat there. Even being a chain I’ve never seen additions like corn.
If you tell my mom that a sancocho has potatoes, carrots, or corn she’ll scoff that Dominicans love to copy things (with additions you might find in other countries) when we already have superior sancocho. 
She feels very strongly that sancocho must have three meats (pork, beef, and stewing hen), but will accept two (she favors pork and beef if you must forgo one). Growing up I never saw things like smoked pork chops or ribs in sancocho, but it seems to be more common in recent years.
Vegetables strictly plantains, yuca, yautía (which is taro, but there are four types and mom tends to include yellow, white, and purple), and ñame. Pumpkin is used for color and thickening the broth but not left in pieces, though occasionally I see some sancocho with a few bits of pumpkin. Lots of people skip some of the types of yautía and ñame since the cost adds up and sometimes you can’t get your hands on all of them.
Colombian sancocho tends to have fewer starchy veg (plantains and yuca typically included along with potatoes, and sometimes pumpkin in large pieces, but not the others), and always has corn that I’ve seen, which makes sense since they consume a lot of corn overall. They also use spices like cumin (a very unpopular spice among Dominicans) and achiote for color.
Btw my mom loves to express discomfort about my charcoal grill producing smoke when lit and bothering neighbors, and I have to point out to her that people here regularly light firewood on the sidewalk next to their homes to cook big pots of sancocho, along with the music blaring, so surely me lighting my grill on my yard is not worse than that. 