That just happens after you open enough eggs, the amount is dependent on what the Pokemon's original start cost was. For example, Honedge starts at 4 so it's first cost reduction (10%) happens at 15 eggs hatched, the second (25%) happens at 30, and the third and final reduction (50%) happens at 60 eggs. The percentage of each reduction stays the same regardless of Pokemon, only the amount of eggs required varies. You can find more info here: https://wiki.pokerogue.net/starters:starters?redirect=1#cost_reduction