The way I see it is, there are some people who have been farming IEs and grinding AP for months to get their neck level up. Many of my twink friends spend over 8 hours a day in IEs in order to get their necks to 34. And then this 110 boomy up here does 3 expeditions and jumps from neck level 20-something to 34? And expects to keep it?
And in regard to 120s, there is a neck level leaderboard, in which some people have somehow managed to get over neck level 40. But if someone who was neck level 35 from casual dailies/IEs got lucky with a few of these gems, he/she could have jumped up to the top 10 spot with little to no effort.
Sure, Blizz screwed up by letting this happen. But it makes sense to remove the gains, considering many people have put hundreds of hours into grinding their neck level and suddenly get surpassed by others who “got lucky”.