Google took the Tesseract OCR engine, one of the first engines, and wrapped document analysis and some high level improvements on it. In the current OCR market landscape there are only 4 commercial engines, and two that make up 98% of the market. Compared to those two OCROpus is not even close because of the legacy engine. So the real reason is it's old technology, very old. Unless Google licenses ABBYY or Nuance they will not get any better. The reality is OCR takes 50 man-years to develop to compete with these top two engines, and it's just not practical for even Google to go out and start from scratch.