That is a great question, thank you for stating your opinion.
My answer is this...
Most of these new #tribes that want their own interfaces just need to get up and running quickly as this is a new idea.
Steemit is open source, therefore putting your own spin on it is simple. Steemit is also the most familiar UI and very easy to bring in users with.
Once things smooth out post-launch, surely some will alter their UI’s. @appics has already done this.