The game doesn't have a set chance for each outcome. Instead, each one has a, let's call it, base probability. For example, Lucky and Frenzy have base probability 1, Click frenzy has 0.1, and Cookie chain and Cookie storm have 0.03.
When you get a GC, the game compiles a list. Each effect has a chance to be added to the list equal to its base probability. Then the game chooses randomly from it (with even chances).
So overall chance to get a specific effect is complicated and depends on some conditional effects (chain/storm require 100k cookies, dragon effects require auras, building special requires having 10 buildings).
Due to this, and the fact that chances on GC page are outdated, I suggest we replace them with base probabilities and, optionally, a brief version of this explanation.