I don't find myself convinced that BA cannot make money flying from outside London - they just don't want to. You can make figures prove just about anything, the old adidge about "lies, damned lies, and statistics" applies equally to accountancy in so far as how you choose to apportion costs governs whether an operation is deemed profitable or otherwise.
That might be true if you want to make profits vanish to reduce your tax bill. BA made continual gaping losses at their regional bases, and these couldn't just be adjusted on the balance sheet to look like a profit. What was amazing wasn't so much that BA became LA, but that they hung on in the regions for so long, even trying the BACON rebranding exercise and so on.