It's probably out of habits. Like, we call it "creation gear" or "mendacity gear". Well, for that to stay as it is for the whole expansion, they need to shift the tomestones and get new names.
It's also a good psychological game design tool to reinforce the feeling of progression. "New name = new stuff".

So, while it doesn't really have any gameplay reasons, it still has some perks of its own. And since it's probably quite easy for them to do, might as well keep it.