Long time TNG viewer & lurker here - first time post.
OK. back to the original Black Hole topic:
Uh... anyone else wonder why they had to drill to the center of the planet before creating the artificial black hole?
Not saying these are THE reasons, but pick or choose any of them:
(a) LIMITED SUPPLY
Nero did not know how to synthesize "red matter" from decalithium - only use it - so he had a limited supply - (beach-ball sized)?. In the Countdown comics, the Vulcan black hole generating tech was a closely guarded secret. And I'm assuming Spock never divulged that secret when he was captured. Since Nero kept the the red matter in the Jellyfish, rather than construct his own red matter container reinforces the fact that he did not fully understand the theory behind it - he just utilized the tech - like a good miner would.
Remember, he had a whole lotta Federation planets to implode and every drop counts!
(b) REVENGE FACTOR - POETIC JUSTICE?
he wished to completely erase both Vulcan and Earth, just like Romulus was completely erased from memory by the Hobus Supernova.
Being a miner, only a complete, thorough job would be acceptable.
a temporary misplaced black hole on the surface may leave alot of bread crumbs flying around
(c) Location. Location. Location
If Nero DID not carefully place the temporary black hole in the center of the planet he might affect the other planets in the solar system. Remember this stuff was designed to contain an exploding sun. Much like the controlled building detonations in city skylines, Nero wanted to make sure he did not jeopardize the other planets. Remember he was planning to wipe out the Federation, the Klingons (see Countdown) and possibly Cardissian empires. And if they are gone, who will pickup this prized real estate such as Mercury mineral rights once the other big boys are gone?
That's right.
Romulus uber alles.