Because letting the game decide legitimized the amount, accessibility, and location of the minerals, rather than it just being something you make up.
I personally might request that survey ships be able to carry survey teams around that they automatically drop as part of surveying. Then they wait for the team to finish, pick em up and move on.
It's a bad idea in the near term for feature creep reasons I think, until Steve at the very least gets a test game going, but in general I would argue this might be nice.