It's ineffective because very little is done. Sure, they say it's over 2 billion hours per year, but let's think about that a minute.
I live in an area where there is a lot of rural territory. You have to get out, take the door, get back in the car and drive down the road maybe a 1/2 mile to a mile before the next one. It's not uncommon to fill up a minivan with 7 people and do that for a morning. When all is said and done, that's 21 hours logged among them all and how much time was spent going to a door, maybe 20 minutes?
I believe of those 2 billion hours, it includes the Bethel workers slaving away for the Organization, again, no preaching to anyone is involved with that.
JWs get to count time to do relief work when there is a natural disaster. Sure, they may informally witness here and there, but again, very little preaching is done in those scenarios.
At a new Hall build, let's say there are 100 brothers and sisters working a 10 hour day. That's 1000 hours logged for the day, and no preaching was accomplished.
Take 2 people standing at a cart sipping coffee and looking at their phones. 6 hours logged and maybe only a conversation or two.
All the family heads counting time doing family worship. Their wife and kids could be baptized, but they still get to count all that time, 4 hours per month.
When one looks at the reality of it all, you can see how very little is being done. Jehovah can't bring the end until the good news has been preached in all the inhabited earth. Looks like he's gonna have to wait a few more hundred years at this rate, or maybe Jehovah will have the stones cry out!