Welsh was banned because Wales was annexed into England Proper by Henry VIII--good old Welshman Henry Tudur himself! Also, the crowns were united under the Scottish King James VI.
You must remember also that not all the Scots are Celtic. Some are descended from the Scots who came from Ulster and others from the original Brythonic Celts (especially in the southwest), but many were Angles (the southeast) who never spoke a Celtic language. In act, the Angles were in Scotland every bit as long as the Scots were! (It's all very confusing because today the "Scots language" refers to the English of the Lowland Angles and not to any Celtic language.)
The banning of Gaelic, bagpipes, tartans, etc., in the eighteenth century was due to the Highlanders support of the Stewarts over the Hanoverians. This was not, as some seem to think, a war for Scottish independence but a war to place a Stewart back on the throne of the United Kingdom.
England is now 80%+ of the population and my guess is that there are more "Scots" in England than in Scotland. Ditto for the Welsh. The perils of Empire -- the first English Empire was in the British Isles before spreading to the rest of the world.
This point is well taken.
True.