The author literally spells out why this isn't always the case:

> Yes to start out it’s 95% booleans. But then you want a rollout. And then you want some targeting rules. And then you want non booleans… maybe some json. Oo wouldn’t it be nice if the json could conform to a schema… and then eventually you are like damn I really want to change these without deploying. Or you want to read the same flag from multiple services.