Organic Chemistry: E2 reaction mechanism?

So I have an exam in Ochem Lab tomorrow, and while I was studying I got confused. The dehyrdohalogenation of 2-bromo-butane with potassium tert-butoxide gives 1-butene as the major product (same for KOH). Why is that? trans-2-butene is more stable, and is the major product in the E1 reaction, but why is the primary hydrogen more easily abstracted than the secondary hydrogen in the E2 reaction? I understand the E2 mechanism just fine, but not really why it favors the less substituted double bond. Sorry if my question doesn’t make any sense…