I think there is more to it than Polar Bear = Arctic animal and Muskox = Arctic animal.
One major difference between the way of life of muskoxen and polar bears [for as many there are] is that polar bears are rather aquatic. They are such well insulated animals that they can overheat in the wild, yes even where it's very cold for people... so the water works as a cool refuge. And so it does also in captivity, even in warmer places.
Whereas, muskoxen do not swim usually and do not live on polar ice.
Their original range was limited to parts of north-eastern Canada and eastern Greenland, though they have been able to survive as south as areas of central Norway... by latitude it corresponds to a part of Canada which is mostly uninhabited [think Yellowknife] though it also corresponds to a good smattering of fellow Scandinavian nations Finland and Sweden. Whereas... Pennsylvania's latitude is similar to that of Spain, the Balearic Islands, Italy, the Balkans, the Caucases... the places where Europeans go to enjoy sunny climes and indulge in hedonism. These areas are rather warm and dry. Kentucky whereas has a latitude similar to Syria, northern Tunisia, and Malta - which are all sunny places though with some level of precipitation. [Kentucky's currently at 30+ degrees right now... how do you think a muskox will do in that clime!]
Whereas where muskoxen live in the wild, climes are rather cold. And there is usually a decent difference between the warmest and coldest temperatures of the day. A typical day this time of year in Nunavut's capital, Iqaluit, has a high of 12 degrees C [or 54 F] and a low of 7 degrees C [or 44 F]. And things are mostly similar in Greenland and other Canadian settlements in muskox-country. Admittedly Oslo and Yellowknife are rather warmer... but then they are the southern extent of the muskox' range. So alas, there is almost nowhere in the United States with a clime required for the proper husbandry of the muskox. An unfortunate reality... with a silver lining.
If you have a US passport then it is still possible to indulge in the joys of muskox without having to leave the country. Alaska is, as you may have guessed, the one state with a similar latitude to the areas they are historically native to. And with the proper climate, multiple zoos in Alaska do maintain muskoxen; and there are also dedicated farms in Alaska which breed muskox. That is to say, the zoo-managers in the warmer states have learnt better than to maintain this animal which would be climatically inappropriate... it only makes them look like the Ultima Thule and the muskoxen are having Nunavut!