>>96361377
It doesn't do much to encourage it for sure. The complete removal of narrative rules is another step away from it and KT21 already wasn't great at it. Fixed teams and specialists have done a lot, I think, to actually remove the need for players to make up their own stuff, because even though the new teams have much more detailed rules that are cool they remove the need for the players to come up with those special things themselves.
And then tournaments of course aren't going to be helping, since those there are encouraged to value performance in the mechanical side over the fluff. Nobody will want to spend even a few minutes of their tournament match time and brain juices on discussing the lore of their team vs the opponent, and the matchmaking in the tournament won't care who matches up against who.
Just do it if you want to. Borrow inspiration from the loose motivation examples in KT21 - my kasrkin are munitions caretakers, so no matter who I face I can throw some story together about them wanting ammo resources or materials, and that story can be put together whether my opponent wants to collaborate on that story or not, because it doesn't depend on anything in their lore. I once faced ultramarines veterans with them with crystals as objective markers and figured that those crystals were important materials for specialist bolter shells that both the ultramarines and the deathwatch team my kasrkin supplies would be interested in. My opponent didn't need to do anything which was great because he was focusing on learning the rules.