Thanks for assembling this post, it was a very interesting and informative (and maddening LOL) read. As for the question:
Why the switch? Why did Jehovah's Witnesses start distrusting archaeology so much and start claiming that it is only "weak" Christians who need archaeological evidence as a "crutch" to help support their "shaky" faith?
Well, I imagine it's because this is no longer a field where they can "pick and choose" in a remotely credible way; the amassed knowledge has tipped and come to contradict their foregone premises more often than it supports it (and is now accessible and available to anyone who chooses to seek it out). When the body of knowledge grows and shifts such that typical JW picking and choosing can easily be shown to be absurd, the only thing left to do is attempt to discredit the entire field, either subtly or not so subtly. I suspect they will continue to pick and choose out-of-context snippets that fit their circular and ignorant arguments though, much like they have done and continue to do with other scientific issues such as evolution.
Thanks again for compiling and posting this, it was well presented.
Edited to say: Too many words! The short version of what I was trying to express here is, if the information doesn't fit with the JW conclusion, then the information is automatically branded as bogus, period. Which of course is exactly backwards.