New ranking of how transparent the think tanks are

From Transparify.com, a new report:

“We visited think tanks’ websites and looked at the funding and donor information disclosed online, including in online annual reports. Institutions rated with the maximum of five stars are highly transparent about who funds them. Think tanks with four stars are broadly transparent; typically, they do not disclose the precise amounts given, but instead group their donors into several funding brackets. On the opposite end of the spectrum, the funding of think tanks with zero stars or one star is highly opaque as they fail to disclose even the names of some or all of their donors.”

And the results for the UK are here (other tables are available for other regions).

Note TJN’s position. Also note the position of rather anti-tax, anti-government players in the “highly opaque” category near the bottom: Wikipedia describes all of them as either “right-wing” or “free market” or “libertarian”, or some combination of those. Given that secrecy is the enemy of properly functioning markets, why might this pattern be apparent?