It’s just for safety issues in areas of high crime. When they start locking the doors in the suburbs, then you will know the heat is on.
Someday there may be an announcement to get to your local kingdom hall at such and such time. If you’re not there on time and they lock the doors, then you’re dead meat just like in the days of Noah.
In the case of the members of Speke, Liverpool congregation I think they'd be safer at home. The locals would rob the teeth from your head if you gave them the chance.