To quote you from higher in the thread, "But it seems to be in their long term interest to have a fair, balanced political system and liberal society as we have now in the US." Is buying a news paper to promote that idea not a form of activism?
The WP has covered various union's arguments against Amazon, eg: https://www.washingtonpost.com/news/wonk/wp/2017/07/17/why-t...
I think you may misunderstand what left-wing people generally think. This quote from the above article summarizes it quite well:
Jon Leibowitz, a former Democratic chairman of the Federal Trade Commission, said the agency has a duty to challenge any deals that could end up hurting shoppers.
“Think about the Amazon business model — that’s typically bringing down prices and enhancing innovation, which is a benefit to consumers,” said Leibowitz, now a partner at the law firm Davis Polk. “But the FTC is a very professional agency, and they’re going to pay attention to any substantive concerns raised by outside parties.”
https://www.poynter.org/2016/whats-life-at-the-washington-po...
It is possible that a well run, honest, independent newspaper is still a viable business model, if guided smartly in the online environment; maybe Bezos really just believes that? If so, then robust editorial independence would be part of the business model.