Engineering is not about achieving perfection. It's about organizing compromises to create a product that provides good utility at a fair price. These were not oversights or mistakes they were intentional design decisions.
Likewise.. you can see segmented memory as "nonsense" and a "waste of development time" but Intel clearly didn't fail at anything. They've been one of the largest and most successful chip manufacturers for decades, because their products provided real utility at affordable consumer prices and software developers gladly put up with the technological choices to be a part of that giant market.