Maybe because it's not normal? (but not illegal) Dealing with ruts is one. They can only handle that when they are with omega or by medications. But I think it's more on social norms.
Maybe it has something to do with pheromones? Since his reaction was so strong to the pheromones. But I agree it could also be social norms
In some it's dominance, one has to Submit To the others phermones, which is against alpha Nature
In the og LIAI side stories we can see that non alpha/omega pairings go through many difficulties bc they can't satisfy each other's needs. Betas can't help omegas or alphas on their cycles and can't mark e/o. I guess the same applies for 2 alphas or 2 omegas with the addition of clashing pheromones and the aplha instinct to assert dominance. Despite this love always wins so they'll sort it out!!!
I think since alpha are the dominant one and omega are submissive when an alpha bring out their pheromones to another alpha it's to dominate another show them who on top. So maybe that's what siwoo means when he says byul doesn't know what it really means to date another alpha. Since he only dated omega he wouldn't know how to handle an alpha. At least that's what I think. I think it's also the fact the siwoo has such strong feelings for byul that he doesn't believe that byul will ever by able to reciprocate them and eventually leave. Since in siwoo eyes byul always moves onto the next thing. So now he trying to cut off the last thing that connects them
Does anyone know what it means when two Alphas are dating? Like, why is he making a big deal out of it?