Is not possible to get a efficiency 5 in diamond tools while enchanting. Netherite and Iron tools works, I suppose wooden tools works because the issue is being creating in some numeric management that Minecraft does when getting the level for tools. I do not think this is the original intention, I rather see mote accurate having netherite tools not being able to enchant with efficiency 5 or either having diamond tools capable to enchant with efficiency 5.
For recreating this issue in vanilla minecraft you can either test for along period until you are in a really small change for been a coincidence or you can make some RNG manipulation and get the same conclusions as I did.
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This is caused by enchatability values. Netherite is more enchatable, which also means you are more likely to get higher tier enchantments.
Netherite being more enchantable than diamond is intentional as per https://www.minecraft.net/en-us/article/minecraft-snapshot-20w06a
Diamond tools not able to receive eff 5 from an enchantment table is also very likely intentional.