Because it's really, really difficult. A lot of AI-ish stuff pretty rapidly gets to the point where it _looks_ quite impressive, but struggles to make the jump to actual feasibility. Like, there were convincing demos of voice recognition in the mid-90s. You could buy software to transcribe voice on your home computer, and people did. And, now, well, it's better than in the mid-90s certainly, but you wouldn't trust it to write a transcript, not of anything important. Maybe in 2040 we'll have voice recognition that can produce a perfect transcript, and human transcription will be a quaint old-fashioned concept. But I wouldn't like to bet on it, honestly.
And voice recognition is arguably a far, far easier problem.