Well I am one of the many disappointed people to see pebble go, so please do take this into account.
So here it goes, I haven't read any article on any site technology or business that can make any sense in the Fitbit purchasing pebble story.
Actually Fitbit products and os are incompatible to say the least with pebble's, and also pebble wasn't, at least not yet, a bankrupt company.
To my mind this move appears to be an effort to remove a certain player, specific products, from the market. Especially the new pebble products were not to be allowed to hit the market. To my mind especially the pebble time 2 which was very similar to specific competition products.
It's true that the smartwatch market is shrinking and the smartwatch is becoming a nitche product for specific high value customers, pebble's high quality and low pricing was heavily hurting that.
So here comes the hard part, I believe that Fitbit was "payed" by specific two market players to purchase and kill pebble. And in our today's business world the word payed has of course many ways and meaning's.
I of course have no proof of this and it's definitely an assumption, but what would you think...?