

Are you confusing Scots and Scottish Gaelic? Scottish Gaelic is the one that’s spoken in the western isles, Scots is across most of the rest of Scotland, including big cities
Scots is hard to tell from English sometimes because Scots has undergone near language death, where it adopted more and more features from English as it was taken over, and Scots was regarded for a decent while as nothing but bad English








I’d also guess that the large number of vowels in English has to do with it, General American English has around 16 vowels (counting both monophthongs and diphthongs, other varieties of English have similar amounts)
I feel that when there’s that many vowels, the exact quality of the vowel is less important and thus they can shift around more