Last time TT had a direct balance update: [5.11](https://na.leagueoflegends.com/en/news/game-updates/patch/patch-511-notes#patch-tt-cs), _four years_ as of the 10th next month.
TT never gets targeted missions to encourage people to play it, which SR and ARAM do. TT does not allow you to gain Champion Mastery Tokens. TT has decidedly been left _out_ of targeted balancing, which ARAM has received, despite ARAM being a casual mode meant to be just for fun with no ranked. There is no focus on competitive TT at tournaments. Riot chose to spend time attempting to make Nexus Blitz happen rather than improving one of their _existing_ permanent game modes to make it more desirable.
"Barely anybody plays it!" Because Riot has systematically refused to give people a _reason_ to play it. And I will forever be disappointed by this.