I’ve had some time to breath and rethink how I explain this in a way that it doesn’t make it sound like it’s a personal want. So -
Achievement’s are a means to display that you’ve done something and know how it works if its a content based achievement. Mostly end of expansion Heroic farm runs require you; for some unwritten reason, to link that you’ve achieved “Ahead of the Curve” before they will allow you into their group.
Using my earlier example of the “Not in My House” achievement, when I link that achievement from Ravij in game it will say that my character “Ravij” earned it to anyone who clicks the link. But in fact it was an alt that earned this achievement. Ravij has never completed this achievement before as seen here when I mouse over the points part of the achievement.
Why then am I not being credited for these points if I can link it and it says I’ve complete it on Ravij when I haven’t? This is what I mean by asking for achievements to be truly made account wide. If one character earns it, they all should. The achievement UI is filled with sub UI’s that it shouldn’t need such as mousing over the “points part” to see which character earned the achieve.
To answer the question of why should a lvl 10 have the lvl 70 achieve? Simple. WoW is built on the fact that a lot of players expect you to know everything before you step into any form of content. A person playing a low level alt and interjecting into a conversation they may find in shout chat (as many of us often do) will get bullied based on the “compare achieves” that many higher level “elite” players tend to do to silence people they think have no idea what they are talking about. “Compare Achieves” Only lists what that character you’re on has achieved (I believe this is the way it still works.). Making achievements truly account wide is a a benefit that will end this form of “comparison” harassment.
I’d like to also add that there are achievements you earn based on how many times you have done X amount of thing. Many PvP achievements are like this such as “Win 100 Warsong Gulch Matches” or for PvE “Pop 1,000 Tumors in N’zoth Assault Areas” These achievements are already tedious in themselves for some and I know a few who would want the achievement total to be counted across every character. Say you’re at 50 wins in Warsong Gulch, but your character is no longer meta in BG’s or you want to PvP on a different character. To earn 100 wins achievement you have to start from ground zero on that alt. It is also the same for continued achievements. Say you completed the 100 wins achievement and are now on the next tier of that achievement that wants you to get 1,000 wins. IF you start on an alt, you have to start from scratch aka get the 100 wins before you can work on the 1,000 wins. This has to be done with every alt and just like the 100 wins achieve the win count is not carried between your characters.
Creating account wide achievements for scenarios like that encourages people to play their alts instead of forcing them to play one character for what seems like all eternity.