edit: Oh and I absolutely think Paradox fucked them over big time (legally) and in some shape or form delayed Bannerlord a LOT, so their shitty MP Warband clones had a chance of success. Luckily they split up not that long ago.
Oh, I was not aware of this. What happened?
It's all speculation and I would have to go do some digging to put a complete timeline together. But while it was clear TW were working on a sequel and even after the uneventful announcement of Bannerlord (an empty teaser trailer with a press release saying nothing), there was zero press, none of the developers talked about Bannerlord at all.
It wasn't until the split with Paradox that they started doing the dev journals and so on.
I think there was definitely something going on, either stalling production itself, or a gag order on production updates.
Paradox published Warband to (I would call it that anyway) great success and then proceeded to have another company make one clone of its multiplayer part after another. (War of the Roses and War of the Vikings) Even at the time I thought it was a major dick move towards TW, but people were happy to see some games trying to do the same thing as Warband.
People sometimes say that developing With Fire and Sword, Napoleonic Wars and Viking Conquest took away from TW's resources they could've devoted to Bannerlord, but I think the sum effect was minimal. They did help with the port of WFaS to the Warband engine and did support it with patches for some time, they did help with patching of NW and VC, but all these games/DLC were made by separate teams who licensed the engine, TW were working on Bannerlord at the same time.
As I said, it's my speculation that something went seriously sour in the deal with Paradox. Another possibility could be that they did waste time and somehow forced Paradox to drop them, but it sure as hell didn't feel like it - everything loosened up and things actually started happening with Bannerlord, after they split up. (the way they announced it too, seemed quite happy about having the power over their games back)
edit: quick Googling:
January 2008 - TW sign on with Paradox
March 2010 - Warband release
October 2nd 2012 - War of the Roses is released.
October 29th 2012 - Bannerlord announced.
November 22nd 2013 - First Bannerlord dev blog released
January 2014 - TW and Paradox split up.
So the first blog was released before they split up officially, but I think it's safe to assume it was already decided at that point.