Why!

[Morningstar1337]

To answer your question. I say that there are two factors.

The first of which is that there are many methods of getting Anima weapons at a certain, and while they at least include one item bought with Eso, they are not the only method.

the 2nd is that the Eso thing was used in all steps because the previous relics also used Tomestones.

Additionally, the Relics are the designated Grind Weapon, as in you are not suppose to set multiple weapons to the highest stages easily. (See, pre-nerf Atma Weapons, where Low Drop Rates made it nigh-impossible for one player to get more than 1 Atma weapon, if they got any at all)

The Unidentified items can be obtained from all Beast Tribes bar Ixal, as well as ARR Hunts and Maps. Patience is key here, because one way or another you're going to wait until you can get all your relics to the same level.