The charitable answer is that it's positioned similarly to NY/SFBA relative to the rest of their respective countries.

The answer I really believe is that Hired is a for-profit company, this report is content marketing, and it would be bad PR with respect to its London clients for it to put London in Tier 4 below the likes of Philly and the Twin Cities.

Right, it seems London at 101 and Toronto at 92 USD pull down the averages of both those groups significantly.