From a Talent Development standpoint, there are a few red flags with Kean that perhaps explain the decision.
I think while he is a talented player, he seems to have reached a level that he's comfortable with and hasn't shown much desire to push on. Whenever he's been challenged with playing a different role or adapting his style of play, it always seems like he's not been up for the challenge. Compare that to DCL who had to play a variety of roles and did so with enthusiasm and it's a red flag he won't progress.
From a few articles in the Athletic with regards to the culture of the club, it's evident they are looking for very team orientated players and it's difficult to see Kean fitting that model. Rodriguez could also be seen as perhaps outside that ideal, but the class he brings is worth it. Kean didn't demonstrate that x-factor that would be worth making an exception.
It's difficult to put any stock in reports about his training performance. Without sitting there and watching it or looking at his GPS data from a session all we have is standard PR pieces.
I’d say his mum being there when he signed was an early red flag - one of those tricky concepts to explain but the more distance between a players working environment and the parents tends to be indicative of a player who can be developed better (with exceptions of parent coaches).
Would probably be a fascinating case study.