Because there's diminishing returns on effort for each feature and some features just don't fit well with in plan9. And sometimes there's a workable alternativ

Because there's diminishing returns on effort for each feature and some features just don't fit well with in plan9. And sometimes there's a workable alternative. Lastly, it's really not for general users. It's for (academic?) computer people who are dexterous and willing to try new things.