The neuter pronoun refers to a concept, idea, something already talked about. It doesn't refer to a specific noun.
In your sentences, the demonstrative pronoun appears before the concept (found in the subject complement (predicate noun)). Since the demonstrative doesn't have an antecedent, it must be used in neuter form.
This answers your question, but it doesn't mean that everyone agrees. Generally, if you're not talking about a specific noun (one already mentioned, one you're pointing at, or one that's inferred), the neuter pronoun is usually used.
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