Top-notch mountain trekking shoes are advertised as having Vibram soles. They are supposed to be durable and have superior traction on wet stones, mud etcsetra.
This is what we want from na mtb tire, right? Then why no vibram tires?
Vibram is simply a brand name for rubber soles made by Vibram S.p.A. of Italy. The actual composition of the rubber and the lug design used differs across their product line, with specialized compounds for hiking, industrial use, and for their "Five Fingers" barefoot running shoes.
They began as a manufacturer for hiking shoes and were one of the first to make them with rubber soles, which helped them become a well-known brand in that market.
The manufacturers of MTB tires are continually experimenting with new rubber compounds and balancing durability, weight, and traction. I'd expect that Vibram S.p.A. doesn't see much opportunity in becoming a bicycle tire manufacturer.