Well, at the time it was highly expected that London Zoo would receive them when the discussions were first made in the mid 2000s, and was supported by the mayor at the time - Boris Johnson. Colchester also expressed serious interest.
Maybe the term fluke could be applied generally anyway as it was the current political climate at the time that allowed it all to happen, I could elaborate further on this but back then diplomatic relations between China and the UK were experiencing a “golden era” of cooperation whereas now it’s quite the opposite.
It was an unlikely coalition of the likes of Nick Clegg and Alex Salmond who made it happen, including the RZSS management at the time comprising of eccentric (but brilliant) individuals such as Ian Valentine, which is most likely why it went to Edinburgh as opposed to London.