I don't know officially, but BrightScript was the language developed for the BrightSign line of digital signage products that came out prior to the Roku streaming player (now it's split off into a separate company). I suspect having a working custom scripting language already in-house played a very big part in the decision making on that. The original Roku player was actually strictly meant for Netflix. They probably developed the original Netflix channel using BrightScript prior to realizing the potential for the device. Once Roku split away from Netflix, it was likely that using the platform they already had in place was the quickest way to market.
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