Ok i found their input:
Blizzard
Hey all,
A quick update on changes to Holiday Loot with the launch of ‘Love is in the Air’ today:
When we changed Holiday dungeons to scale based on a player’s level, we aimed to increase participation in those dungeons. We also wanted to avoid a situation where a player with an army of low-level characters had a better chance at receiving account-wide rewards than a player with one or two max-level characters. At the same time, we didn’t want to impact the amount of chances that players who maintain several max-level characters had in previous years.
As a compromise, we made account-wide rewards a random drop for any character capable of participating in current-expansion content. For the remainder of Legion, players level 98 and above fit that criteria. The minimum level requirement will increase again in Battle for Azeroth, and will continue to increase in future expansions.
I think one contradict the other (highlight parts) and put more effort on players while this wasn’t the case from Cata to the end of Legion, so basically players that got it before have it easier compared to players looking for it now. If they put a limit like 50, it’s not an army of low-level characters as they mention that there was an issue, that never existed.
They just increased the time sink for players and players that did it before got it easier.