Hasbro might think they've done enough. They've done a ton of episodes, have branched off with EQUESTRIAN GIRLS, and have a 2017 film in the works. I feel they feel they have pleased fans, and made lots of money.
The only info we have regarding season 7 is this...
" Leah Jade in early March 2016 after meeting with DHX tweeted that "season 7 of MLP is in production" and in mid-April 2016 stated that she would remove said tweet if not OK to post. Later in mid-April 2016, Jim Miller was asked regarding the matter and replied, "We're still working on 6!", and Jade removed her relevant tweet. On April 29, 2016, Miller was asked, "Do you know if there will be a season 7 of mlp?", and replied, "That's Hasbro's decision to make." -
Source