breach atlas nodes is +98% chance to contain breaches - why not 100%

having specced into expedition and breach, expedition I can acquire 100% chance, "Your Maps contain an Expedition Encounter". but for breach the most i can get is 98% - why not make it 100%?

it'd make sense if breach was part of the content that had a 2% baseline chance of spawning and expedition wasn't - but my understanding is that expedition also has a base chance of spawning.

nevermind.