Hello there,
Actually, your 2-methyl-but-1-ene is labeled incorrectly. The double bond gets priority, so it should be 3-methyl-1-butene.
To answer your question, since this is an elimination reaction, we have to consider beta hydrogens. The major product (2-methyl-but-2-ene) would be formed moreso over the 3-methyl-1-butene. This is because if the reaction proceeded as a carbocation, the tertiary carbon is more stable, hence creating a major product of 2-methyl-but-2-ene. The minor product is only a small yield because upon elimination of a beta hydrogen, a secondary carbocation would be formed (the relative reactivity of carbocations are 3>2>1.
It's not that the minor product is not formed at all, but it would be in a small amount compared to your major product.
