The pregens have limited information on them so you can play them "out of the box" almost immediately. You'll notice that Kyra only has one orison listed, too. And that there are other things you can do on your turn mentioned in the Combat chapter that aren't listed in the What You Can Do On Your Turn of each pregen.
Why the wizard have 4 cantrips at level 1 instead of 3 like the CRB?
For the sake of simplicity. With only 4 cantrips in the Beginner Box, and wizards in the Core Rulebook getting 4 per day at level 2 and higher, there's not much point in adding the complexity of having a "at 1st level you choose 3 of these each day, but at 2nd level you get 4 so that's all of them" rule. Might as well just give them 4 cantrips at level 1 and let them focus on the other, more interesting aspects of the class.