Because it was rushed as shit. I don't care about the wedding, I wanted to see Ruby and Sapphire grow as actual characters, and them being sprayed was a great opportunity for that. But they skip that entirely, solidifying the fact that they're totally codependent and there's nothing more to them than their obsession with fusion. It doesn't help that the Diamonds were underwhelming as fuck after being hyped for for entire SEASONS. If this was another show it would've been ripped apart, but since this is SU of course the fanboys lap this shit up.