Interesting developments, just watching.
In order to break the Katy-Rihanna alliance with a lot of friendly celebs and bases
(it was basically all bases versus the pre-Artpop Monsters), Taylor is trying to build her own alliance. If necessary by snatching from Katy, the catch is: To whom are they truly loyal? Is she getting an useful chess piece or a rotten one Katy should had disposed years ago?
Let's look at it from Kanye's point of view:
If he thinks that Kim made his friends ditch him, because they feel too good, upper class,... to be associated with Kim. He still has the alliance not judging him for loving Kim. Maybe that's why he is domesticated/timid when Katy is near. Offending Katy/Rihanna probably means a lot of fan bases turning against him on a global scale. However can his ego/narcism accept his position
(the rapper who was featured on a Katy song and on a Rihanna song) in the alliance?
Taylor is recruiting and Kanye wants to check if the grass is greener on the other side. Katy knows that there is no point in trying to force someone to not leave and wonders if it's going to be messy. He can afford to interrupt, expose,... Taylor, because the backlash is limited. Thus he let go of the brakes and seemingly Taylor has no other choice than taking him in.