11 to 13 years is a huge span of time and no game takes that much time to be developed. Think about that in the 2000s such a "small" studio released M&B (2005 in beta, 2008 in full) and puny two years later (from the latter date) it completed another game (M&B W), so it is pretty unlikely that after earning very considerable income said company has been working on a project for that long due to reasons other than just prolonging the creation artificially.
well dont expect much, overhyped things are failing in close years around - for example star wars, warcraft, game of thrones, vikings ...
its most likely some interior issues the taleworlds company has that takes development of bannerlord soo long, either money or social contacts & quarrels