I think the reason is that the game isn´t further ahead yet. Iron is required for basic things like tools or a work bench. So it needs to be available in a good amount and not hard to find. At the same time there is no metal detector in the game yet and neither caves - both would make it easier to find ores in general.
The iron boulders were introduced in the past because there was no world generation yet and still people could craft stuff for which they needed iron. Now its a bit different but i think until there are other means to find bigger ressources of iron ore these boulders are okay. Even later on its okay, maybe just less common or not in every biome.
And after all its just iron. No other ore type has such boulders so whatever happens, you still have to look for the other ores.
If the ores were removed now and you have "only" low or medium availability settings for ores some people could give negative reviews or quit the game because they can´t progress fast enough.
For now its alright id say. Later on maybe just reduce the amount of iron boulders.