The Baby Pokémon all fall under the "Slumbering" category because they, well, sleep like babies!
Rock-type Pokémon (Slumbering), naturally, all sleep like rocks!
The nocturnal Dark-type Pokémon are naturally light sleepers (Dozers) at night.
Why can you still find Pokémon with the Abilities Insomnia or Vital Spirit dozing? Because they still need sleep, just that they can't fall asleep in battle.
You can only have 5 helper Pokémon at once when normally in other games the team limit is 6 because the Snorlax you bond with each week is taking up the 6th team member slot (assuming you don't have Nightcap Pikachu).
Before the introduction of Lapis Lakeside, the islands all correspond to the four seasons: Greengrass Isles (Spring), Cyan Beach (Summer), Taupe Hollow (Autumn), and Snowdrop Tundra (Winter).
