Why doesn't BitTorrent use hash trees?

[Matthew]

There is a proposed extension to BitTorrent that would add support for hash trees.

This would allow all torrents to have trivially small piece sizes, with only a single hash value in the info data.

It uses SHA-1, but it would be better if it used TTH.

This obviously would be a major improvement.  Why has it never been implemented?  Obviously, it would require a new torrent format, but I don't see any reason it couldn't be done, with clients having backward compatibility.

[dueda]

One of the reasons is the slow evolution of BT. As an open source community changes drag; as a Cohen's initiative it's stalled. News eventually come from a few adventurous developers - Tixati, Koinonen, etc, but BEPs are slow. Main problem is to define what is important: What to focus on, where to?

Privacy, performance, decentralization, centralization, interaction, monetization, or what? Looks like pirates and users can't agree with each other and disagree amongst themselves, and torrent/file-sharing future is uncertain (future generally is).