Thanks, Wonderment for the post.
Two reasons why a modern Heb. NWT makes sense:
1. Modern Hebrew ≠ ancient Hebrew. Languages are always changing, and not just with additional vocabulary. Look at how different KJV English or Shakespearean English is from modern English. That's only 400 years ago. Go back to Chaucer in the 14th century and then Boewulf before him, and the English is almost unrecognizable.
With biblical Hebrew we're talking 2000-3000+ years. I've spoken with modern Greeks and they tell me that they cannot understand the NT when it is read in modern Greek Orthodox services. It has changed that much in 2000 years.
2. It is much easier to control the R&F if you've got one translation issued by the authority of the organization they are all obedient to and trust.
We all know how the WTS is obsessed with control.