Some items cannot be disenchanted (does this apply to other professions as well?). Examples w�ould be the the oh-so-famous Twilight Cultist Robe or the level 90 boost starting gear.
Endless Wowhead list

Some work being done to fix this issue: 6ccef15

Note that wow.tools is deprecated and we'd need to find a different solution for that before we can feasible merge this.

Because of the endlessness of the list, and the fact that wowhead has an incomplete version of it, getting and storing that amount of data is not feasible.
If someone would find a good way of retrieving such data in a simple manner and it would prove to be accurate, I'd gladly add it, but currently it's just too much work to be worth it.