You raise an important point I had not considered. Bots could skew trending metrics to favor spammers. That could get them more media coverage which could lead

You raise an important point I had not considered. Bots could skew trending metrics to favor spammers. That could get them more media coverage which could lead to influencers trying to get in on the coverage by re-tweeting spam. And the spammer succeeds. Unlike Google which mercilessly penalizes content farms, Twitter probably does not have the intellectual wherewithal to combat spammers.