Not just Disney, but Eurocucks too. These extremely long copyright terms were the norm in Europe long before they came here and European artists would bitch and moan endlessly that the U.S. wouldn't have European-style copyright lengths. This was eventually changed with the Rome Convention.

Doesn't matter who's responsible for it, all the big players in the industry benefit from long IP terms. Disney probably just got tired of being the one footing the bill knowing that if not them then someone else will pay for the lobbying for endless IP. Steamboat Willy and the original Whiney the pooh aren't worth much so it was seen as an acceptable loss.

I figure what they're hoping for is that whoever ends up acquiring WB ends up footing the bill for IP extension lobbying once Tolkien's work's start nearing the public domain