"He will undercut what authorz make by low balling them."
Goodreads is just a place where readers discuss books. It has nothing to do with what authors make or don't make.
"Bezos hasnt disclosed what he paid"
News reports say it is about $160 million with some possible bonuses attached depending on whether the site meets certain targets putting the upper range around $200 million in total.
"The web site haz 16 million 'subs'"
So Amazon breaks even at about $10 per sub. Sounds like a pretty good deal.
"but it will decline and errode, and will never make any money"
Ha! Where will 16 million people go? Amazon already owns all the competing sites. People don't tend to move around that much, they tend to stay put in the communities they've gotten used to.
Only some ignorant short would think that the goal is for the site to generate its own profits. Everyone else understands that these things merely generate more sales of books and that Amazon will make $billions in book profits in upcoming years.