I've read quite a lot about myths and history, but for some reason I've neglected my own heritage, namely the 'Celtic' sphere. Something I'm finding incredibly strange is the complete lack of reference to Scotland in books about Celtic myth. More specific than this is the idea that Welsh and Irish medieval texts are the only source for understanding Iron Age Celtic beliefs and stories from the past generally. This doesn't make sense. Despite all I've read, I can't find a single answer. It's one of those issues that's so large that it really is frustrating me. This is the problem:
Scotland was/is a Celtic nation. It was comprised of Gaels (Scots and Irish) as well as Picts and Britons (both of these latter are Brittonic speakers, but they're still Celts of course). Yet despite reading several books on the topic of Celtic myth and general British history, I haven't actually found a single stated reason why the only texts ever written are from Wales and Ireland. For example, in one book all about the history of Scotland, the author continually states the Welsh preserved everything related to The Old North (Goddodin--literally Edinburgh and environs) but no answer is ever given as to why it's Wales alone that did this.
I'll be honest, it's kind of insulting, but more than that it's frustrating as I feel like there's a huge gap in my knowledge which should be easy to fill. I'm reading a book called The Celtic Myths (a very general title) and it's entirely based on Wales and Ireland, as if Scotland doesn't exist. It appears to specifically avoid Scotland.
Why is there no Scottish version of the Otherworld, Lugh, Morrigan, Cu chulainn, etc.? I would have thought that Scotland shared deities and heroes with Ireland since Scotland was intimately linked with Ireland (Dal Riata). Obviously Scotland has folklore, but nothing like legend or myth written down as in the texts cited below. Apparently the poem Y Goddodin was actually written around Alt Clut... But there's still only Welsh and Irish mythology. When people speak of The Mabinogion it's considered Welsh heritage.
Why is there no Scottish version of The Mabinogion or the Táin Bó Cúailnge? I genuinely can't figure out why there's no primary and important text for Scotland's Celtic heritage. I haven't read it yet, but I know the The Old North and other Brittonic elements are mentioned in The Mabinogion, but what about Gaelic Scots or Pictish elements? I refuse to believe there's no overarching, important Pictish or Scottish (as in the specific Scots group) literature.
I'll put it as simply as I can. I'm constantly reading that Wales and Ireland preserved everything, but no one seems to be saying why only they preserved it. Why is Celtic = Irish and Welsh?
Sorry if my tone comes across as agitated, but it really is a bit annoying to not know why my country has no part in any Celtic literature when it clearly should. Let me repeat, this isn't a nationalistic rant. This is just someone wanting to understand history and literature.
Edit: To make my point even clearer, even if you search for Scottish mythology you'll find only references to Irish mythology in which Scotland plays a part but it still falls under the umbrella of Irish mythology. Even the Fianna, apparently with strong links to Scotland, is still mostly about Ireland and Irish people with Irish names. I'm struggling to find a single Scottish work of legend on the level of famous primary sources. It's not even the feeling of being excluded, I'm wanting to understand why Medieval Scottish people didn't write anything...
The problem is that you're viewing this from the perspective of someone in the 21st century who (presumably) speaks English as their first language. Our ancestors in Ireland and Britain would have viewed the world very differently.
If we're to go back to the 5th or 6th century for example, there is no Wales, England, Scotland, or Ireland. Each of what we think of as distinct nations today were instead a collection of different kingdoms that warred with each other. There was no Welsh, Breton, or Cornish. At the time, all three regions spoke the same language, as did their compatriots in what would later be western and northern England.
Similarly, the Gaels didn't differentiate themselves as Irish or Scottish. You mention Dal Riata, that was a kingdom that straddled both islands. A Gael living in northeast Ireland was going to have more in common with his cousin across the water than he would the Gaels living in the south of Ireland. The languages would have been part of a dialect continuum and largely the same (in the written form) until the 17th century though even today they are mutually intelligible.
You can still see this distinction in the Gaelic languages. An Irish speaker might say they speak Gaeilge but they'd refer to the Scottish variety as Gaeilge na hAlban. There is a shared identity and heritage.
Cúchulainn is a Scottish hero as much as he is Irish because he was a Gael. He actually undertook part of his training in Scotland according to legend. It's a similar story with the rest, they're Gaelic legends. Scotland was a mix of Gael, Pict, Briton, Angle/Saxon, Viking but the Gaelic side of its heritage is what it shares with Ireland.
Sources:
The Isles - Norman Davies
Wars of the Bruces - Colm McNamee.
Scots Mercenary Forces in Ireland - Hayes McCoy