If I recall, imploding the respective suns into a Black Hole of the Red Matter's creation (remember folks, Red Matter doesn't create a supernove, it creates an artificial Black Hole) would not take quick care of either Vulcan or Earth.
It would plunge them into cold and darkness but folks wouldn't die instantly and the planets would physically remain.
I suppose he could have just dropped it onto the surface of Vulcan and the same job would have been done..................but that's pretty dull.
It's kinda like wondering why the Borg thought going all the way back in time was easier than just flooding Federation space with dozens of cubes simultaneously (which is what I would have done if I was the Borg Queen).............it's a thread you can pick at, but do you really want to start picking? Because then you just realise how fast the whole thing always unravels in Trek.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist