Though ever since Wrath this has been confusing players, so, as suggested back then, removing the 'BoA' tag and replacing it with 'Heirloom' would possibly have prevented at least part of the recurrence of this topic.
The suggestions to make Heirlooms buyable by each character, a scroll down menu etc. would prevent Heirlooms from being Enchanted, and as the primary purpose of current-style Heirlooms is allowing wellfare twinking to stomp newcomers into the curb - while kicking out real Twinks that require real effort - all suggestions that would prevent Heirlooms from being Enchanted are 'causing technical difficulties' and other blah-di-blah.
That's all there is to it.
Besides being logical deduction from what actually happened over the years (e.g. Enchant Cloak- Stealth gets an enormous buff right when the Heirloom Cloaks are introduced) , it's one of the few explanations that actually makes sense. Heirloom Shields are now in the books (coincedentally after they massively upped a certain Shield Enchantment), something that isn't needed by any stretch of the imagination with the trivial tuning of the game - unless you want to encourage wellfare twinking and stomping newcomers.
Tinfoily? We're talking about the same people who e.g. introduced CRZ for gankfests.