manycookies asked: Not that plainswalking is an all-star mechanic, but I feel the "You can't sneak on a plains, hence no plainswalk" idea is kinda narrow in creative interpretation. You don't have to be sneaky to bypass an enemy line. For example, plains have a lot of freedom of movement, ideal for fast but not necessarily maneuverable/all-terrain creatures like horses. A gazelle or cheetah wouldn't thrive in a jungle, but give them an open plain to run in and they'll never have to see their enemies.
Since my silly answer hasn’t been received too well, I’ll try a less silly one. Landwalk is tertiary in white’s color pie. White is the color that least becomes unblockable. If it wants to get past blockers, white takes to the air, it doesn’t sneak past.