As described above, some versions of Windows require drivers to be signed proving who made them. For this to work Windows needs a list of CAs trusted to issue the certificates. Whether "I am not paying somebody £100 for a cert" constitutes a valid reason is arguable. But that seems to have been their plan here.

"was needed in the days of Windows XP for a signed driver, is no longer needed" doesn't sound particularly overt, or malicious.