I don't know and couldn't guess the reason, but given they're staking their credibility and potentially putting themselves at risk of retaliation (see: Sony), I suspect they think they have a good rationale for saying it.
Perhaps it could be to gain a bit more trust or respect from researchers (targeted or otherwise) and/or certain customers/users, or perhaps the US government encouraged them due to some geopolitical calculus, or maybe it's part of some plan that only makes sense because of some private knowledge known to few.
Perhaps it could be to gain a bit more trust or respect from researchers (targeted or otherwise) and/or certain customers/users, or perhaps the US government encouraged them due to some geopolitical calculus, or maybe it's part of some plan that only makes sense because of some private knowledge known to few.