I can't tell you where it started, but I can tell you it's certainly extremely common, as I've heard it from both current and former zoo professionals over the past few years. I certainly would've thought that it would be extremely difficult, if not impossible, to move a 17ft bull, interesting to hear that it might be a lot easier than I thought.
It helps if your area has a lot of big (rich) zoos with giraffes and coordinated breeding programs and can support animal transport companies (or zoo departments) with their special giraffe trucks and skilled staff.
In whole Europe, only about 3 or 4 transport companies move giraffes (overland). And they can and regularly do take fully grown bulls, only fee for them will be higher. The recently retired head of transport department at Dvur Kralove transported around 450 giraffes himself (in 40 years), with zero losses.