You only have so many slots for 3 drop coloured cards and a lot of the alternatives to this offer a much more powerful effect
For example, red the color of passion, freedom, emotion, and BURNING EVERYTHING TO THE GROUND is very good at destroying artifacts and throwing fireballs in peoples faces but none too good at dealing with enchantments
My personal favourite of this is Rafiki, Ethereal Guide and Tigger, In The Crows Nest, for their fantastic expressions
Facilier, Agent Provocateur, she has a slightly higher six willpower and a juicy three lore when she quests
These cards see play across multiple archetypes in the Pauper metagame, which makes them staples of the format
The fact that you can bounce a blocker and then still get to play a creature on your second main can be huge for most aggro decks