The "rummage" mechanic is actually very "red" in nature. Blindly throwing away something you don't need in the hopes of getting something better is as red as red can get.
It's also worse, unless they start at least templating it so that discard isn't part of the cost.
In general, the color pie is both amazing, and also broken. The color pie is defined in such a way that it gives certain colors (*cough*blue) enormous advantages and huge scope for powerful effects, while shafting others pretty badly (red, and until pretty recently, white).
There's also a lot of "legacy" effect in the color pie. Plenty of mechanics have reasonable flavor justifications for going in colors other than the ones they are in. Taxing counterspells could have gone in white. Bounce could have gone in red. They've mentioned some of these themselves, and it was seen in Planar Chaos. But because early in the game certain mechanics were strongly placed in certain colors, they've stuck around that way.
They have done SOME major shifts over the years, but most of it is from colors other than blue, the color that needs the most pruning. For example, artifact & enchantment destruction went from heavy primary in white to heavy primary in green. One-shot mana cards went from black to red.
An easy way to see this at work, beyond the obvious fact of blue-centric decks being far and away the most successful across all formats in Magic's history, is to play monocolored EDH decks in each color. It's a good illustration of just how janky and limited a lot of white and red's mechanics are. Whereas, amusingly, certain mono blue decks (Arcum, Azami) are actually stronger than almost all multicolor decks.
