>>37120967>>37122335-They evolve from the same pokémon because they represent celestial bodies (irl, not in-universe), that's why Cosmog is the nebula pokémon. On top that Cosmog's description of a bag of dust that fits with one of the steps for the magnum opus (the creation of the Philosopher Stone) according to the Emerald Tablet. Cosmog's dex entry says: "Even though its helpless, gaseous body can be blown away by the slightest breeze, it doesn't seem to care" while the Emerald Tablet says "The Sun is its father, the moon its mother, the wind hath carried it in its belly, the earth is its nurse.", this is also why Solgaleo and Lunala (in alchemy the sun always represents the man and the moon is the woman) breed Cosmog in the planet. They live in the space between parallel timelines (the Ultraspace) but when they breed they leave their child in a stable place until it grows.
-Likewise, Cosmoem (what comes after the nebula pokémon) is the protostar pokémon, he probably represents the proper Philosopher Stone as well, specially considering its shiny palette is RED like the stone, and this red sticks to its evolutions as well. In fact, Solgaleo, Lunala and Necrozma represent 3 of the 4 process of the ultimate transmutation, nigredo (the putrefaction, the death, Lunala), then albedo (the purification, the life, Solgaleo) and citrinitas (yellowness, transforming silver into gold, this is Necrozma's purest form, the golden Ultra-Necrozma). The fourth and last stage is the rubedo, the redness that gives the stone its color.
Oh and Solrock and Lunatone not being in Sun and Moon is probably a joke
