Why does the groudon page say Solarbeam is better than earthquake?

Due to the meta. Grass type is doing much better than ground type coverage. For example, using Groudon solarbeam on Groudon raid would be a definite plus.

- best neutral damage moveset
- ground moves are comparably weak
- ground doesn´t have much use, while grass has
- his overall stats are murderous enough to make him a good "grass" attacker

Since I want to power up a Groudon, too, I thought about his movesets aswell and came to the conclusion that I want to have double Ground instead of Solar Beam, just because Groudon is the best ground attacker by far, while he has some trouble to compete with the best grass types (+ I already have enough good grass attackers). Besides that, it feels just wrong to give a ground type a grass move