Why is anti-Markovnikov regiochemistry primarily observed in hydroboration oxidation of alkenes?

Question

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The first step in the hydroboration oxidation of alkenes is the addition of borane to the double bond. This step is a Markovnikov addition, meaning that the boron atom adds to the carbon atom that is already bonded to the most hydrogen atoms. However, the second step of the reaction, the oxidation of the borane adduct, is an anti-Markovnikov addition. This step is thought to occur via a concerted mechanism, in which the boron atom and the hydrogen atom that is bonded to the carbon atom that is not bonded to the boron atom are both transferred to the oxygen atom of the oxidizing agent. This concerted mechanism results in the formation of the anti-Markovnikov product.

Why Is Anti-Markovnikov Regiochemistry Primarily Observed in Hydroboration Oxidation of Alkenes