From what I read, majority of the focus of page bytes reduction to optimize fro mobile experiences is on lowering JPEG image quality (AMP Lite) and/or fixate it

From what I read, majority of the focus of page bytes reduction to optimize fro mobile experiences is on lowering JPEG image quality (AMP Lite) and/or fixate it to 85% for AMP. I wonder why Google is taking a fixed reduction of image quality reduction rather than considering a dynamic image quality reduction approach like JPEGMini[1] and Kraken.io[2] took? The latter ones will take visual perceptions into consideration hence they are usually able to squeeze out more bytes savings in the end. [1]: https://www.jpegmini.com https://www.jpegmini.com [2]: https://kraken.io https://kraken.io