Do they? I haven't seen anyone confused by that in a long, long time. Just like all other blocks, people don't know if the block melts-- until they learn it. People don't know which mood cobblestone is safe on either, until they learn it either by asking or by looking on the wbm list. I disagree with the fact that ores shouldn't melt: It adds an extra challenge to always look around in caves + it makes sense to have something valuable (like ores) melt to me + it's always been like that. I don't see why ores specifically would need to be safe.
Well, what are you going to do with ores anyways; not use it to build a house but break it/smelt it and not use it for houses. I don't understand how it adds an extra challenge if the cave is already getting flooded. I doubt there is any map with a one block wide wall with ores. Secondly, why would the blocks of the items (lapis block, iron block) not melt but their ore counterparts do? Under your logic, it would mean that ore blocks should melt because they are valuable too?
Also, nobody will ever remember a long spreadsheet with what blocks to melt and what not. The only blocks you would memorise is the main ones and the only way to get ore blocks is through silk touch, which no one except for the very rich have. Cobble is safe on Calm but not safe on Annoyed, but ores melt on ANY mood. People forget that ores melt, because they think it's more durable because it contains stone and blends into stone and therefore shouldn't melt on Calm. Yes, people can learn and memorise it but most of us won't; and will both make Mods' life's better because less people will complain from a natural flood from a ore block and also make our lives easier because we won't have to remember that ores melt, every single time.
