Be careful what you wish for
> stop children getting easy access to hard-core pornography
So if you were a smut-propelled website, making your living from mucky ads on dodgy pages and suddenly you found that a goodly proportion of your income had gone, due to the UK's new filters - what would you do?
As a provider you could start advertising: but if the filters are still in place your customers are blocked just as surely as before. You could give up and get a proper job - though I don't know what, errrr, openings there are for ex-sex workers trying to go "respectable".
Or you could make your website look like an ordinary one, so that the sirens¹ don't go off any time someone clicks on your URL. Of all the alternatives, that last one seems like the most successful ploy for continuing to lead your life in the style to which you've become accustomed.
But: there's a downside. Not to you, or your pervy punters. The problem is for everyone else: who hasn't opted out of naked viewing (on the screen, not in front of the screen). Since you've tweaked your website to avoid the filters of poverty, it's now far more likely that people who aren't searching out pleasures of the flesh will stumble across your website without any warning, so successful is your filter-busting camoflage. You never know, your mother might even discover your real occupation!
So while porn-filters sound like a good idea, ultimately they might have the opposite effect: by requiring the less salubrious websites to appear mainstream, it would be more likely that visitors wouldn't just be people actively looking for stimulation, but ordinary folk who found them by accident.
 the audible kind, not the ones that lure unwary travellers to their doom - though maybe that's what porno websites will do.