It wouldn't have worked because, since when in Final Fantasy has a magic spell just been stopped by throwing a bomb at it? Sephiroth could easily use the Lifestream to invoke Meteor again in the highly unlikely, and ultimately impossible scenario that Meteor was interrupted. Sephiroth is in the Lifestream. It's at his beck and call. He can absorb it, and use it to manipulate materia and magic. But it wouldn't matter because Meteor can't be stopped, it's magic.
"Meteor" isn't a real life, reality-based meteorite that just falls onto the planet.
It's a Black Magic spell. A manifestation of magical force. Unknown magical energy draws in planetoids and asteroids, binds them together, and draws them to the planet so that it may impact the surface. Detonating the largest bomb you can imagine on that object would do nothing. As witnessed in the scene when the Shinra 26 does collide with Meteor, any damage that's inflicted gets undone by the force binding Meteor together. It cannot be destroyed by simple mortal means. It's a destructive spell that's been invoked and must be undone/negated by Holy.
The Huge Materia's value is the lives, knowledge, spirit energy and magical power that is contained within them. Would you be comfortable if humanity just somehow took the entire Amazon Rain Forest, compressed it into a glass object sphere, and then hurled it into space to blow up an object, which would ultimately fail?
It would be gone forever. And that's why blowing up the Huge Materia would be foolish and destructive. Huge Materia obviously has material, spiritual and planetary value. They're one of a kind. They're unironically, the closest equivalent to the crystals of FFVII's world. And they actually do bestow power to the heroes once they actually master their materia. They're more useful as powers given to the characters than just one-time use bombs that do nothing.
