I wonder if the slower decline of JWs is due, in part, to the door-to-door work they did for so long.
To be clear, JWs don’t have a “slower decline” than other churches. They are increasing while other churches are decreasing. That’s not slower, that’s opposite directions. And yes, door to door preaching must be part of the explanation.
Another common mistake is to say that JW growth is below population growth. But that’s not true either. World population growth is now under 1% per year. Apart from a couple of years, JW growth has been consistently higher than population growth.
I have been expecting JWs to start declining for decades, but it hasn’t happened yet. I still think they will probably start declining at some point, maybe within 10 years, everything else being equal. But then who knows what will happen in the world in general, with wars, climate change, AI, pandemics, and more, and what impact all that could have.