You're not being honest by saying mortality is the only difference between Warband and Bannerlord NPCs. And you assume a lot and use those assumptions in lieu of arguments. However, even if I were more inclined towards the "hating Bannerlord" mindset, it does not make me automatically wrong. Despite whatever you might think.
They [BL NPCs] do the absolute bare minimum, and it shows. Majority of players don't care about BL lords because of it, too. As some above mentioned, they have so many systems they could draw on to improve this but for some bizarre reason, do not. The new marriage system, the child system, clans etc. They could easily remark upon the player about these things, or make them attend marriages or feasts for example, in which they recall later. But they don't.
Because the Bannerlord NPCs are, in fact, bland and lifeless.