Sovereign nations do employ significant signal intelligence resources to defend their government. The Chinese are heavily invested and have been responsible for the majority of attacks on US IT infrastructure for years. It wasn't discussed openly before because the trade relations weren't degraded/ing like they are today.

In case you've missed the memo, they're threatening all of their neighbors outright with kinetic military force. Japan is no trivial country to threaten force against, so the diplomatic climate has changed and more information is being shared publicly in anticipation of an outright military conflict.

There are conflicting interests between individuals that lead to physical fights and the same applies to sovereign nations whose interests run contrary.