I've personally worked for multiple startups where rolling out hardware keys did not require making additional IT hires (we're talking about companies smaller than ~50 people). Perhaps at BigCo size, you end up needing dedicated personnel to support a hardware key rollout at that scale, but at that scale you have the budget for GitHub Enterprise anyway so the point about pricing is moot; at BigCo size there is also even more of an incentive to roll out hardware keys since you're that much more likely to get spear phished.