Scab-Clan Mage

From what I read on the card is I cast a spell. It gets +2/+2 and 1st enemy creature gets -1/-1., so why when I cast spells when there are bo enemy creatures does neither trigger work?
Had this is multiple instances.

Example Equisite Firecraft opponent..nothing.
Use Consign to removes some pesky Thopters....nothing.

but if the enemy has a creature to target it works right.