It's strange to see the lack of variety when it comes to npcs & bosses, dungeon set-ups, skins/cosmetic stuff in a game this old... Is it a choice from the developers and artists to refrain from adding new and refreshing content such as new enemies or new dungeon environments? Or is it simply not a priority/ forgotten about? After all, the fact that only a handful of the many mounts in the game have a decent amount of skins seems kind of sad this long after release...
They developers added a TON of new content to the game a few months ago. Faction Warfare is awesome now, Crystal Spiders, Avalonian Loot Bots.
They also announced changes coming. I would check out Hardcore Expeditions if you wanna try new "safe" PVE options.
Send me a friend in game:
The devs are always and are still working on incorporating new and exciting content, however as it is a fairly small team working on the whole thing, only one thing can be done at a time
Regarding skins: At the moment there is a fairly even schedule of 1 new skin every referral season, aside from the ones that you can only buy from the cash shop.
Although I absolutely understand that everyone wishes for more of them faster, in my experience SBI values the quality of vanity items over quantity and thus will take their time with the release of new ones.
If you would like to know what kind of major updates are planned for the near future, have a look at the last Dev Talk.
Hope that this answers your question a little bit