> You still need a physical machine to access "the cloud", so don't you still have all the expensive problems related to managing a fleet of PCs, but now you have to do it x2?

Microsoft Intune/Endpoint manager is actually pretty easy to setup/enroll laptops. Autopilot takes a bit of work, but it does get you to the point where IT doesn't have to do anything on a new laptop shipped to a user.

Ultimately if you don't want your users doing much on their laptops you can make it pretty simple to manage them.

> Is data security so important that some companies are willing to pay 5x hardware costs and 2x maintenance costs for it?

It really depends on the industry. Most folks aren't doing this because security isn't a priority.

Some firms may not survive a data breach, others might incur tens or hundreds of millions of dollars in costs (directly and indirectly) for one large breach. These folks do care and will spend whatever it takes because it's got a business justification.