You'd probably need to check or ask on GitHub why they didn't go with that option.
Building a new front end to steem to maintain a single topic is outside the skillset of the majority of steemit's userbase.
It wouldn't be for one topic. If it was just about one topic, it wouldn't be the major disadvantage you said it was. If there is a demand for this feature, the Steem Blockchain and codebase is quite open for someone with the skills to fill this demand.