I wonder if the emphasis on task management is a contributing factor in it not taking off. Anecdotally, most places have a task management system already, switching systems is a heavy cost, and building a good one is actually a ton of work in the long term.
I'd be interested to see an app that focuses more on the culture aspects here – kudos, user profiles, events, search. Most companies don't have solutions for these, and bringing them into one place could be valuable.