When the ROK fell crashed into the San Cantor Hive some 800 years ago, along with the other damage, a lot of the forwarned population were already evacuating the habs. Thus the death toll was lower than otherwise might have been, but the noise and pressure wave were immense.
By the end of that war, the continent of Benq was still left with between 400% and 500% of the usual deaf population for the number of persons on the planet. One of the main focii of the resulting efforts of the Ecclesiasty was returning these persons to a useful role in society. This was aided by the large mechanicum presence and many persons with augments went on to do many good things.
That was eight centuries ago; the association between the deaf and the church persisted a long time and with the churches involvement in births, deaths and marriages, somewhere along the line 'deaf' was misheard. Or perhaps willfully transcripted incorrectly. On Devos IV there are a number of shrines to the Cult Imperialis; those run by the Sororitas inevitably have a cadre of assasins.
These ladies are Hasslefree. Paint by Golem.