But it's not spam. If fifty people you follow retweet the same popular post, you do not want to see it fifty-one times. You want to see it once, and you want it ranked highly because everyone you follow thinks it's an important post. It's a form of crowdsourcing from a curated group of contributors. The chonological view cannot accommodate.
That’s more of a problem with Twitter’s design. I don’t want to see any “retweets”. If someone I care about replies to something then (optionally!) show me their reply. If I find that compelling I can follow the primary source. I do not care about regurgitated content.