If the language in question has decent reflective capabilities, then I'd question why they don't use it. Perhaps they ran some benchmarks and found the language

If the language in question has decent reflective capabilities, then I'd question why they don't use it. Perhaps they ran some benchmarks and found the language runtime performance lacking or maybe they are implementing the ECS pattern to the letter (e.g. using an integer to represent an "entity") as opposed to implementing ECS as a concept.