The difference is that Solar Charms are supposed to be result-oriented toolset Charms. They are straightforward, focused in narrow niches of utility and extremely useful when applied. Solars are supposed to be the simplest Exalt-type to play and thus need the simplest and most newbie friendly Charmset to match that desire. The answer to “How do I build a Solar who does X?” should be “Buy the X-doing Charms.”
All the other Exalt types are supposed to have a variety of quirks in their design which make them less newbie-friendly but more interesting in their playstyle. You are supposed to play Sidereals to have the experience of being given an extremely limited toolbox and trying to figure out how to solve complex problems with it; Sidereals are puzzle games. You are supposed to play Infernals to have the experience of being given an extremely powerful toolbox, but being forced to have to act in very specific ways to access that toolbox, Infernals are like morality games in that every choice you make defines your character from there forward.