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Reminder that ninjago is THE lego theme
It took what worked before: stupidly overcomplicated lore and mysticism from bionicle, the more permanent cast of characters with simple personalities and traits from hero factory, and builds mixing over the top vehnicles/mechs with simple buildings and structures, along the universally loved theme of ninjas. Also the short films/ movies from bionicle and hero factory being converted into a show also helped.
That's why bionicle g2 failed: you can't bring back something that has alredy been replaced
