Recently I just watched (after millions of times) The Return and I noticed…why did the Covenant send ground troops just to later glass the world? Wouldn’t it make more sense?
The Covenant would search worlds for Forerunner artifacts before glassing them, this is why Reach wasn’t immediately glassed once it was found.
But what about the Covenant attack on earth, they still glassed it before they activated a portal to the ark
Their glassing efforts weren’t on a planet-wide scale, they were searching for the Ark on Earth, or at least the portal to the Ark in which they found
They were glassing Reach to a lower extent before ramping it up, supposedly to crush resistance when searching.
Apparently it’s religious
The process of glassing a planet begins when a [fleet] has achieved air and space superiority on an enemy-controlled world. The specifics of the glassing process vary depending on the strategic significance of the planet or the orders of the [Fleet Master] A [Minor Prophet] or [Minister] is typically assigned to most [Covenant] fleets to oversee the destruction of a human world. In some or possibly all instances, before the fleet is permitted to destroy a planet, the Prophet performs a religious ritual—the Prophet declares by which religious ideal of the Covenant, marked by a glyph, will the world be destroyed. There is currently only one known instance of a human world, [Kholo], having a glyph burned into its surface.
Basically a made up ritual to exterminate all humans life after the prophets found out they were wrong about the forerunners and humans were the successors, psh holy zealots