Why the adjective "custom," then? Why not just say they don't make wedding cakes?
Because they DID make wedding cakes celebrating the time and memorial institution of matrimony between a man and a woman, which at the time was the only legal definition of marriage in the state of Colorado. And they customized them, being able to craft them into works of art per the desires of the couple or wedding party.
The homosexuals destroyed all of that - which was their intention from the beginning.
Because rather than going to the bakery down the street that markets themselves as serving homosexuals - they targeted this one precisely because the owner was open about his Christianity.
They chose to make an example of him and thus create a climate of intimidation for any business daring to refuse serving homosexual celebrations as a matter of conscience and faith.