Why Not Dual Spec.
Sometimes people make a claim that respec fees are intended to be a gold sink, and adding a dual spec feature with a fee would act as a gold sink. Respec fees only act as a gold sink if people are using them regularly. A lot of people avoid respecc’ing due to the fees, so it actually acts as a deterrent, which is a design flaw that should be corrected, not doubled down on.
Additionally, dual spec rewards some classes while punishing some others. Classes whose raid roles are fulfilled with a single spec are not required to maintain multiple builds and gear sets, and are free to use an additional spec for their liking. Other classes are required to maintain more gear sets, and additional PVE builds, rather than the “play as you like” style that can continue without a dual spec, but with lower respec fees.