Also, in terms of waste not want not, I might prefer to seek out diamonds from structures and mobs, without mining the ore, until I can get fortune, but that's not always feasible.
The same goes for obsidian since it requires diamonds to mine. If it's possible to make an enchantment table without mining diamond ore, then you can potentially use fortune on every ore, removing the question of 'I don't have enough diamonds from my first ore for a pickaxe!'.
But of course, that means going through the effort of finding and defeating structures and mobs and making the enchanting table which also uses diamonds, so it may not be worth it.
Finite as diamonds are and worth maximizing, they're still easier to find more of, especially post 1.20.x where they became more common near bedrock.
Albeit again, you can get fortune through fishing and trading, and of course trading was by contrast nerfed in 1.20.x as a counterbalance to diamond ore increases, to encourage mining more and trading less perhaps.