When compared to most of their predecessors, there really weren't too many Legendary Pokemon in Pokemon Scarlet & Violet at the time of their release. None of the series' pre-existing Mythical and Legendary Pokemon could be caught at launch either, meaning that players were limited to just six Legendaries to begin with; two of which were version-exclusive Pokemon.
Pokemon Scarlet & Violet: Every Mythical & Legendary Pokemon (& How to Get Them) [Indigo Disk Update]
When compared to some of their predecessors, Pokemon Scarlet & Violet are a little light on Mythical and Legendary Pokemon at launch.