Goodreads wasn't "the future of book reviews", it was a good review site that might have innovated great new things or might not have at all. But regardless, Amazon should never have been allowed to acquire it -- it was incredibly anti-competitive. Amazon never wanted to do anything with Goodreads at all -- as demonstrated by the fact that it hasn't done anything. It was a purely defensive move to prevent anyone else…
Unfortunately that's exactly why so many startups get bought. Not to become part of the parent company's business, no, just not to become a competitor later. Would stronger (and enforced) anti trust laws be a solution? I believe businesses would just lie and say they are going to be part of the business but then just bury them anyway.
Everything that gets bought gets sold as well. The founders of the companies are willfully and eagerly selling the companies they created. Who are you to ban it? Then you have to chain them to their desks and force them to try to dedicate the rest of their lives to the business.