Maybe someone with some brain on The Guardian realized if you're browsing through Tor, no way you're going to create a login and link your browsing to a name/email address...
That makes it sound like no one of The Guardian has a brain, it's not the intention, it's my most trusted news source, but maybe someone on the IT department thought a little bit further.
More likely Tor was set up years ago and receives no attention unless it horribly breaks; and so nobody notices nor cares that ads aren't working there (and if they were they'd probably not get paid for them anyway).
That makes it sound like no one of The Guardian has a brain, it's not the intention, it's my most trusted news source, but maybe someone on the IT department thought a little bit further.