Most likely because Solasta was built from the ground up for D&D whereas BG3 is being retrofitted to an existing game system. Or they just thought it would be easier
I do think thats the case and the current bless is basicly a placeholder. Maybe they took a buff from DOS and reworked it to be in the game, not thinking about the fact that you can pick your targets?
Thats what I thought when I saw the aoe bubble for bless but multiple targets as a possibility for magic missle.
