What ax? I’m the author and a YIMBY. Read the linked article, that’s the exact title of it, and I largely agree with it! I wrote that line because it contradicted the expectations of a movement I myself belong to, which I found surprising.
Land valuation is necessary to implement a land value tax (not to be confused with property tax) which is the main thing Georgists advocate for. Georgists and YIMBYs have an affinity for one another since land value tax disincentives speculation and incentivizes building.