why the National Library of Scotland turns out to be the best place for historic maps of England
I will try to explain:
1. NLS applied for and got scot. gov money (don't know details, some grants) to "digitise" their collection and they didn't spend any of their own money
2. BL (British Library) didn't apply and / or didn't get any gov money (I don't know details, there might have been some grants they failed to apply and / or win, but equally well there might have been no such money pot to win at all), and they didn't spend any of their own money.
That said, there's another, _possibly_ related and fundamental difference: from my personal experience (at least 4 - 5 occasions), NLS employs competent people, whereas, from my experience (similar, several times), BL employees lie to you to make you go away, don't know a thing about their area of "expertise" when finally confronted and, in general, don't give a flying (...). BUT, I don't blame them, as the saying goes, you pay peanuts, you get monkeys. Apparently, the pay is so low, and working "culture" so toxic, that it wouldn't surprise me to be a true reflection of their whole "system".