Clearly that was a very deliberate choice on the part of the Go creators, not the result of oversight or ignorance. I suspect they simply didn't want to reflect the state of the art 30 years ago, 20 years ago, or today. I don't find that at all surprising, because people who want to get things done often like very simple tools which stay out of the way. To each their own though, and I'm sure the go creators would be very happy to see other languages used instead of go by those who prefer more features, more complexity, state of the art from 30 years ago, etc. I do find myself puzzled by the hostility it generates though - it is just a language, one of many, and about which some very ordinary claims are being made (easy to learn etc).
Sure, that's really useful - you guarantee that you can never access the unset half of the value. But it adds a lot of complexity, too. You need a way to declare values of this type - this means more keywords and/or more special syntax. You need a way to then access both halves of the values, so now you have to add pattern matching... that's actually a lot of complexity to add to a language that only has 25 keywords.
All that, instead of just doing what Go already does, which is to return two values and just have a convention of checking the error before the value... which works really well 99% of the time, and doesn't require all the rest of that complexity.