Seems pretty logical.
Again I think people outside of the UK perceive Ofcom to be a censor with a ban hammer. It's an industry self-regulation authority -- backed by penalties, yes, but it favours self-regulation. And the implementation is a modifiable statutory instrument specifically so that issues like this can be addressed.
In a perfect world would this all be handled with parental oversight and on-device controls? Yeah, maybe. But on-device parental controls are such a total mess, and devices available so readily, that UK PAYG mobile phone companies have already felt compelled (before the law changed) to block adult content by default.
ETA: I am rate-limited so I will just add that I am in the UK too. Not that this is relevant to the discussion. There is no serious UK consensus for overturning this law; the only party that claims that as a position does not even have the support of the majority of its members. I do not observe this law to be censorship, because as an adult I can see what I want to see, I just have to prove I am an adult. Which is how it used to work with top shelf magazines (so I am told! ;-) )
I suppose it's not really the done thing to say this, but if you disagree with me, say something, don't just downvote.