I would encourage people to read the NCSC blog post on this as it goes into technical detail on why the decision was made.
https://www.ncsc.gov.uk/blog-post/a-different-future-for-tel...
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https://www.ncsc.gov.uk/blog-post/a-different-future-for-tel...
Bingo. It seems like this is more a bet that they can't become wholly independent without the tooling itself, or can't become independent for a long while. I doubt it has much to do with "setting up incentives for transparency". I think the "will China become transparent about its actions" question is pretty much settled at this point.