Alleria is the leader of a faction and a race, those tattoos likely play a significant role in mastery and employment of the void, which is why it is very likely void elves would have them too. Rommath on the other hand was dealing in fel magic with Illidan and Kael'thas before getting sent back to Silvermoon, his high status, likely means he was near illidari level and powerful enough to require the use of tattoos for containment magic, which is why only he has them, and no other does. And the difference is void elves are brand new, so it could be that it is a thing about them, because we know so little. Blood elves are not new, the transition to blood elves has had a lot of lore and characterisation, and in that time, no tattoos.
Please explain what other logical conclusion and evaluation you can make.
High elves have largely had a rough time, some have been fine in palces like Dalaran, their usual pristine self, but others have been like those in QUel'lithien, and in Kalimdor, had a rough time out in the forest and the wild, little support, they have probably found very tight bonds, with decorative tattoos which elves like as well picked up scars and either not had access to magic to magic them away or have stopped caring faced with the situation of their way faring life.
Face it, it doesn't fit the polished blood elf or dalaran high elf. I'm just observing that.
@
Alanar has a point that such things should be available to all races, but like male beards, guess what, some races will have little to none, while others would have some interesting tattoos, as blizzard will distinguish them.