There is quite a lot to unpack here in your question, but I am going to try to unpack it a bit and hopefully provide you an answer to satisfy your curiosity.

For starters, there really isn't a march of civilization in play, and I'm reading a bit of an underlying assumption that clanship is a more primative form of social organization that is naturally abandoned as a group "progresses". This was once commonly believed, but frankly, "different" does not mean "less than".

Clanship in Scotland got a bad rap particularly due to very long-standing bias against the “men of the mountains”—all the way back to the 14th century, so by the time the term did arrive, English speakers were already inclined to see clanship in a negative light. This was heightened as well by the retreat of Gaelic, which was once the language of the Scottish Kings, to an area functionally bounded by the Highland Fault. However, clanship fundamentally has the same basis as the sort of Feudalism practiced in the rest of Scotland, with powerful families granted land charters and power to enforce the law within their own demesnes.

The Scottish crown did not have the ability to enforce its power on the furthest reaches of its Kingdom, indeed owing in part to geography. While it was hardly impossible to cross the Highlands in the medieval period, it was not easy, either, and the Highlands and Islands were far more accessible by sea. In fact, there had once been a seafaring kingdom of the isles under the earldom of Orkney that did govern the area. By the late medieval period, the MacDonalds were on the ascendancy, themselves ultimately descended from a mix of the norse settlers under the earldom and the local Gaelic population.

Also the MacDonald lords already held considerable land in the Islands, under Aonghas Og, they received further substantial grants of land, including Mull and Tiree, territory held by an elder branch of the same family, the MacDougalls. (If you have seen Outlaw King, Aonghas Og is that red-haired guy that hangs around all movie without really being named) By the time of Iain (John), Aonghas Og’s son and heir, the MacDonalds held most of the land in the Highlands and Islands, from Mull to Skye, and stretching inland through Lochaber, Ardnamurchan, and part of Argyll. A substantial holding, and Iain began to call himself Dominus Insularum, the Lord of the Isles. In Gaelic, that was Rì innse gall or KING of the Islands, an interesting distinction.

We are into clans here without really acknowledging it, but a minor note of etymology. Clan is from the Gaelic word "clann" (surprisingly enough...), which means children. I promise none of this is a pointless side track and it will all come together in the end. Remember that land was held by charter from the King, and this chartered land could be further subdivided (wadsetted or feu lands) by the lord and even further divided by these landholders (in the Gaelic world, these were the fir-tacsa, or taskmen). Holding land in a feudal system is all about maintaining your power, and thus it is important to grant land to close family members and strong allies. So the fir-tacsa (singular: fear-tacsa) were typically cadet members of the lord’s family. In this sort of structure, Gaelic or not, allies also play a major role in maintaining power over land, and thus it is erroneous to believe clans are in fact large families with blood relations. They were formed by a mix of linear descent, marital alliances, and political alliances to mutual benefit. (Thus, for example, the MacMhurichs, the MacBeatha/Beatons and Rhymer families were part of Clan MacDonald.)

None of this explains why we speak of “clanship” rather than “feudalism” when speaking of the Highlands, but it is necessary to dig into the root of your question, namely what was different and why it appeared to persist for a long period after feudal structures collapsed elsewhere.

Among Gaelic-speaking lords (typically English uses the word chief here for the major land-holding nobility and chieftain for the lesser nobility that reported to a chief), the concept of dùthchasis at play. This gets variously translated as birthright, homeland, heritage, etc. We are not getting wildly afield here in terms of ideas, but essentially we are talking about the idea that the land belongs to the chiefly families by hereditary birthright, rather than essentially by feudal land grant from the king. You will still find references to, for instance, the homeland of the MacKays or Campbells. This idea existed, and to an extent persists, even though R.A. Dodgshon, for example, has conducted studies to show that landholdings in the highlands were much less stable over time than the dùthchas would imply.

Coupled with the idea of dùthchas is the idea that the Chief is at the head of his clan the way a father is head of his family (in traditional lines of thinking). This is where the observation earlier of the meaning of clann comes in—it was seen as a fairly apt analogy. The Chief did provide for his clansmen (and women) through various chiefly functions. One of these was the feast held in honour of a grand occasion, and potentially lasting days. It served to showcase the Chief’s wealth and generosity, as well as munificence to his people. The Chiefs also managed their estates (those original land charter grants as well as any additional holdings they obtained by other means over time) in such a way as to balance requirements from each sublet farm so that rents—in theory—would not ruin any farmer. If you are interested in getting down to the real nuts and bolts of how this would look, check out From Chiefs to Landlords by R.A. Dodgshon, particularly Ch. 3.

Edit: I apparently elided a sentence entirely near the beginning.