Well, formulated negatively, it can be said that the Church historically discouraged/forbade cremation because it has been employed by people to mock and deny the doctrine of the Resurrection.
More practically, it is a practice which unnecessarily damages the sacred bodily remains and prevents them from future veneration. So it's much more difficult, if someone should become a saint, to distribute relics of a cremated body rather than bones and significant, identifiable parts of a buried/exhumed body.
It's not like God won't find a way to resurrect bodies that have been dismembered, burned, disintegrated, destroyed, or what have you. He's God, it's no big deal. Glorified bodies are understood to be spiritual, otherworldly, and beyond our imagination, but there's also been a lot of work to describe what they're like and how they work.
Cremation also led to abhorrent practices such as scattering ashes, or keeping them on a mantle, and in modern times, turning them into personal jewelry or launching them into space. The Church didn't like that stuff either. Personally speaking, my dear uncle's cremains are on my cousin's mantle and essentially inaccessible to me, since we're not on speaking terms. I'd really like to visit my uncle's grave, but he doesn't have one!
So even today, the Church forbids cremation if it's for the wrong reasons. But it's tolerated widely because it's often cheaper and expedient.