Can someone with more technical knowledge than me explain why a pilot should be made with unreal engine? Based on experience, I'd guess that the tools Disney has at their disposal are far more powerful. Maybe it was just quicker for a test of concept since Square would be more familiar with that, but I feel like using the tools that they typically use for CGI movies would be far better for an actual series.
UE, being real-time, means they wouldn't need to rent out render farms to make it. Maybe it was cheaper/quicker to develop the pilot this way?