The JWS religion is just another social environment where males meet females and since its in an environment of trust and a subjective imposed identity placed upon the members, marriages occur, some make it some don't.
What may be surprising to many is that the JWS have the same amount of divorces than non-JWS or worldly people as they refer them to.
The JWS leaders will never honestly admit to that fact/truth though.
I would say most of that may come to the fact that people are pushed into marriages for sexual reasons, less for compatibility reasons and that they are forced to marry another JWS.
Look at it this way, a single congregation may have only 100 people in it or less, but the single people there have no choice but to marry another JWS.
The facts relate to whom is the right person for one and another is compressed in this kind of environment.