I think I might have answered this question before and I will link it if I have, but it was years ago and I have learned a lot more since then. I will try to break the answer down into parts as there are a lot of motivations. This topic was actually my undergrad thesis before going onto my Master's years ago. Anyways, let's begin.

In the eighteenth century, Jacobitism declined in popularity after the Rising in 1715 and even more so after the Rising in '45. While the army claimed it a credible threat Jacobitism did not see a wide social spread, not at all like they expected. Once the '45 Rising ended with Culloden, the British government would put out policies to squash out any chances of it happening again. I will get to that part soon. I want to point out that not all Scottish Highlanders supported the Jacobite cause, and the Jacobite cause did not consist of Highlanders. With religion tied to the Jacobite house, it found support in Catholic sympathizers among northern English and Irish, as well as French. I do not have the statistics on hand anymore, but the Catholic population in the Highlands and Lowlands of Scotland had decreased over the decades. British government forces faced the Jacobite army, and the government had Highland soldiers of their own: Highland Independent Companies. These companies were raised and trained by the army and would later be the basis for what would become the Black Watch or 42nd Royal Highlanders.

Between the thirty years of 1745 and 1775, the socio-political landscape of the Highlands changed. The Dress Act most noticeable and known policy implemented after Culloden and while the Act did have some impact on Highland men joining the army to be able to wear their traditional garb, other policies had equal if not more impact on the Highlands. The Heritable Jurisdiction act of 1746 ended the power of clan chieftains over their tenants and clan members. By this time the clan system had already began to dwindle and lose place in the Highlands, the policy ensured it. The government sought out to pacify the Highlands and in every sense make them British. They started with their culture and identity.

The attempt to make them British (sometimes referred to as North Britain) succeeded in a few ways. The establishment of forts and military presence in the Highlands. While the image of forts creates the idea of protection against a frontier or housing a police force, it also gave men another avenue for employment - the military. Stephen Brumwell's The Redcoats touched on this with more depth, but by the height of the Seven Years War, Scots would make up almost a third of the army's numbers. It did not differentiate between Highland and Lowland, but the numbers did indicate an active and large participation by the Scottish population. The war would see the creation of the Highland regiments as a permanent part of the British army. The 42nd Highlanders, 78th Frasers, and the 77th Montgomery Highlanders fought in the American theater of the Seven Years War known as the French & Indian War. The 87th Keith Highlanders, 88th and 89th Highland regiments would fight in either the European theater or the Indies. The wars also gave the opportunity for former Jacobites to show loyalty to the British government. Simon Fraser of Lovat (There are SO many of them) watched the execution of his father, Simon Fraser the 11th Lord of Lovat, who had been a Jacobite supporter during the '45 Rising. Fraser had his lands confiscated and imprisoned for a few years before receiving a pardon. To show his rehabilitation, he bought a commission for a lieutenant colonelcy and raised the 78th Highlanders (previously the 62nd Regiment). Other former Jacobites did the same. By the end of the war, Highlanders had integrated into the military and established their place within the British empire.

When it comes to Highlanders in America, there are a few factors. In North Carolina, the Scots emigrated first in 1736 establishing a community off the Cape Fear river in Campbelton/Cross Creek where Fayetteville currently is. The community saw a steady influx of Scottish families over the decades but increased towards the 1770s. Many of these families came from Argyll and in numbers. These families followed other family members or an influential rich Scottish landowner. However, by the 1770s, many of these families could afford to traverse without needing financial assistance of a patron or indentured servitude. North Carolina offered incentives for emigrating Scotsmen, including a tax break for ten years and low rates for land. However, the government required Oaths of Allegiance from these families, and the Oaths stated absolute loyalty to the King and government. Keep this in mind for later. Highlanders did also emigrate to New York and Georgia, I am less familiar with those, but much of the Highlanders in New York came from veterans of French and Indian War who opted to take lands grands from the government instead of a ship back to Britain. Some of these Highlands settled in the Mohawk valley with the Johnson family, who would be a Loyalist leader in the AWI.

By the early 1770s, Cumberland County is impeccably Scottish with several of the local government delegates having Scottish last names or have originated there. I should point out the naming of Cumberland County is directly from the Duke of Cumberland of Culloden fame/notoriety. The Scottish community remained insulated and kept their cultures. They continued to worship as Presbyterians by and large, they spoke Gaelic, and they kept to each other sometimes resembling the old clan system. The Highlanders in North Carolina did have a social hierarchy with the tenants looking at the landowners and county delegates as leaders. With colonial tensions coming to a head in 1775, the new Provincial government of North Carolina began to watch the Highland Scot community in the Cape Fear region with some apprehension. The majority of them supported Loyalist ideals of monarchy and turned away people trying to change their mind. Whigs could not easily persuade them and every attempt failed, even when they tried to get a Scottish Whig priest to go talk them, the Scottish Loyalists ran the priest out of the community. Scottish Loyalists saw the British empire as a positive to their world and as they belonged to it, they would protect it.

I met Duane Meyer years ago who wrote on this topic in his Highland Scots of North Carolina. I know the various opinions on this topic of Loyalism among the Highlanders. I'm a Carolina Scot. In short, I'm of the opinion it was a variety of reasons but the Highlanders investment in Empire by this time held their support for the King. Secondly, and not so common a thought on the matter, I believe the Highlanders were suspicious of Republicanism and as evidenced by the fact they largely turned out as Royalists in the English Civil Wars. They held grants to their lands. They were quite distinct from the Scots-Irish and "country-born" types having settled this section previously. They were newly settled immigrants. Rebellion wasn't in their best interest at the time. Despite many fleeing Scotland as Jacobites, they ultimately believed in Monarchy as both Biblical and a more stable structure of government. I wouldn't necessarily advocate for these positions but I'm quite sure I would likely have stood with them given their plight. Interesting topic!