It's not just reeeally rare (actually 20%+, but crate also has it's own drop chance) to get a hardmode ore in crates, it also drops random one, not between those you have in the world, but between ALL. So it's hard to make full armor from fishing.
And i hate tin/cooper since they are the loot i get the most. I mean it's obsolete even in pre-hm, so getting those in hm is annoying.