Just like how Apple killed Tumblr for porn problems but gave Twitter a pass
The latter two are "big in ___" apps that are hardly known anywhere else, namely SA, Japan, and China, to which anything HQ in California do will only cause unpredictable and unobservable, likely negative financial impacts. I'm from "Asia" but all I know about WeChat is about as much as that it's a brand with a logo, that's it.
Apple et al allows maximum leniency, budget and local decisions for those local apps because of that. "No one's using it anyway", only cash is coming in, so whatever happens there won't matter anyway, as long as the gig won't stop. Hell, if they need datacenter for all data to stay in China, so be it, if they need extra rapid payments to keep Shinjuku going, so be it.
Tumblr is different; they have US users and negative impacts can be readily measured. So they - its owner Yahoo! US at the time of its death - were not scared to do whatever.