because they completely lose control of that ability when they are in rut, as like omegas in heat, alphas lose control over all their impulses when in rut and cannot think about anything except impregnating the omega they are sleeping with, this also includes extreme alphas. It’s how Yeonwoo accidentally got pregnant with Keith’s baby, without Keith even realising it, in Kiss me liar when Keith showed up at Yeonwoo’s place in the depths of his rut, and how Josh got pregnant and had Pete after Josh and Chase slept together when Chase was in the depths of his rut before the main storyline of Kiss me if you can takes place. Because Dane is an extreme omega, he has perfect control over his pheromones and extreme omega pheromones are the most powerful in the Kiss me universe as they have the ability to completely control even extreme alphas, like we have seen Dane do in the story so far he can use his pheromones to knock Grayson out and wipe his memory, and he can also use his even stronger pheromones when he’s in heat to force Grayson into a rut, on the other hand it takes the pheromones of 5 extreme alphas all working together to force an extreme omega into heat. So Grayson was in a forced rut when he and Dane slept together and lost control of himself and lost control over his ability to stop his semen from not being able to get someone pregnant, in fact when he was in rut and sleeping with Dane all he could think about was getting Dane pregnant. That’s why Dane took the contraceptive because there was actually a very good chance of him getting pregnant.

Aren't extreme alphas capable of controlling their semen so they don't get anyone pregnant if they don't want to? Why is Grayson even talking about hypothetical pregnancies?