Promises made to appease the British as a condition for the handover.

The opposite, HK broke the promise it made to PRC by dragging out implementation of NSL that was always in PRC legal perview to unilaterally implement. The reality is PRC demonstrated stupid patience by letting the HK, the spyhub of Asian operate for 20 years under state of national security exception that any other sovereign would not tolerate. HKers literally had the carte blanche to commit treason (and did), so reasonab for PRC to close that legal loophole after putting up with it for 20 years.

E over post limit

>You can't commit treason to a country no never agreed to join.

As if they have a say in the matter. British Crown handed them over to PRC and turned them into Chinese citizens. Ergo they can commit treason the second they formally draw breath on Chinese soil. Law finally catching up so said treason can be prosecuted, like any sensible national security framework.