1965 or 1966 I first walked into a Soho Porn Shop. This one was close to PR Publications.
The porn on offer was dismal. B?W photos or textbooks made by a rudimentary printer containing a few pictures and bound by amateur methods. Was all there was. B/W porn movies were very rare and usually passed hands for huge prices or shown in dimly lit rooms financed by ticket sales. All that was legal were pictures of topless girls.
And it was so profitable the business was controlled by crime gangs. The shops were turning over $100,000s a year each.
$8 for a set of 5-10 porn pictures or $12 textbooks produced in places the police wouldn't find working 24/7 to keep up with demand.
It was a license to print money and content producers couldn't produce enough of it.