BT doesn't stand for British Telecom any more - in the same way KFC doesn't stand for Kentucky Fried Chicken, and BHS didn't stand for British Home Stores.
Try telling that to KFC
and the last iteration of BHS
But strangely it’s only in the US it is called “Kentucky Fried Chicken”. Everywhere else it is KFC. Apart from Québec when it is PFK.
New BT logo is too bland IMHO. Outgoing one is too 3D however. The new logo will mean the phone boxes are even more out of date. Not that BT Payphones is a core business these days.
Down to cost, I imagine. But I agree with you. Despite them being rarely used now apart from in rural locations with no mobile service, they're a prime outlet for BT's name to be out in the wild without being advertising, so shouldn't still have in most cases the 1991 branding on them. Though perhaps they don't want modern branding associated with something seen as old fashioned.
It's interesting that they seemingly did update the vast majority of modern design phone boxes with the 1991 branding at the time, as I guess they did deem it important that they should have the latest branding.