Why don't alkynes undergo preferential anti bromination to the degree that alkenes do?
From what I know of the mechanism, Addition of Br2 takes place in the following mechanism

For an alkyne, the intermediate would not be stable due to the ring strain on 3 member ring with a double bond in it, thus reducing the rate of reaction.

Mechanism referred from: https://en.wikipedia.org/wiki/Halogen_addition_reaction