If the question is "why can't God", it's because Jesus has already come, the messiah has already come, and that was a promise for only one being.

Now, if the question is "why couldn't God", He could, if Jesus hadn't come and if it were written in His Word.

But have you imagined what a thing it would be? If Jesus hadn't come, 2025 wouldn't be 2025, Christianity wouldn't exist, history would be completely different.