And the problem with that is...? That's why you have to save those brainstorms

.
When you add another creature, you are adding a potentially dead card (because 2 hasty 6/something fliyiers
are enough), and you have to cut something that could search and protect your 'combo' or disrupt your opponent. Those are all much harder needed than an extra creature for the odd just-in-case.
IF you want access te more creatures, run research//development.