They wanted to make the biggest bang they could make. It's great they destroyed Vulcan and killed Amanda, but I honestly didn't have any emotional investment in those versions of the character/planet.
That's a bit of a shame. Besides the necessary younger (not to mention alive) recasting, isn't Amanda exactly the same character? Recreating scenes that are the same, right up until Nero arrives at Vulcan?
The prospect of destroying the Earth (and deaths among the TNG cast) back in the original universe has too much emotional investment. Just to be thrown out there, in a tie-in and moved on swiftly from. It's even worse than Vulcan, where at least there's opportunity to show fall-out and consequences through Spock or whatever might happen onscreen in successive films.