Mark Rosewater has gone into elaborate detail on double-faced cards on his Drive to Work podcast - I would recommend checking this one out for the history of the mechanic
For most formats, there's not much public information available on the individuals who make these decisions, but we do know that MTG's Play Design team has some say in what cards are banned
Boros is best known for being extremely aggressive since red and white are, among other things, known for cheap creatures
Like some sort of fuzzy Pied Piper, Bello can help you quickly amass a board state out of nowhere, swing through for tonnes of damage, and draw more cards than your paws can hold
Theyre another fairly unique artifact name for Gimbal, Gremlin Prodigy, and Roxanne pairs so nicely with Svella, Ice Shapers Icy Manaliths