My understanding was that certain groups of conservative Jews objected as they found it offensive.
That’s a shame, because, far from being forbidden to Christians to use the name, it is very much encouraged:
“For whosoever shall call upon the name of the Lord shall be saved.” Romans 10:13
God has a lot of official names (HaShem, Adonai, El, etc), the Tetragrammton is a very specific one and a very formal one, only spoken by the High Priest at certain times in front of the Ark of the Covenent, and forbidden to be said at other times.
Now, as Christians, I know that sort of thing doesn’t apply, but it sure seems a bit rude to use the name in any other manner than directed by God Himself, so I always thought this was a wise decision.
Regarding Jews who right “God” as “G-d”, the article is incorrect. Jews are not permitted to let the name of God (however written) get defaced, so, in causual writings (like the internet), the word is avoided or written like “G-d.”*
* Learned this on FR from some of our more helpful Jewish Freepers.