I hope you didn't think that the 99.9% figure was supposed to be 'accurate' - it's called exaggeration for effect ... but whether or not most will admit it one of the main motivating factors in a high-control group (like JWs) is members fear of having a reward removed from them. And JWs have it pounded into them at every meeting that they are not good enough, they must do more, more, more, to MAYBE make it through the big A.
Take away the fear of dying at the big A and the vast majority of JWs would cease to be so active in the religion. Take away the stigma of 10 hours a month that must be reported less you be considered 'weak' (and thus 'bad association' and the loss of social status/invitations) and the vast majority would never go in FS again.
Don't try and sell me on the fact that the majority of JWs do this stuff out of 'love' for God or neighbor - I was a JW and I know how they think. <insert> The average JW dreads going in FS and knocking on doors, dreads preparing for meeting parts, dreads going to meetings. Example is when the weather turns bad and so many get excited because if it snows they might cancel the meeting. Or they take advatage of whatever excuse that sounds good enough to stay home from a meeting. There are some die-hards but the average JW is as above.
Oh, and as to if you should be concentrating on your own salvation, NO, according to the JW belief you should NOT be working for your own salvation. It is a 'gift' from God.